Changes include:
* question: Add bootstrap classes to buttons and selects so they look consistent.

* mod_quiz: Add bootstrap styles to report form elements

* question: Add bootstrap classes to question form elements

* And remove the success/fail styles from boost because they conflict badly
with the quiz plugin styles (making unreadable text).

* quiz: nav block buttons had black background

* quiz: Add bootstrap styles to quiz navigation buttons

* qtype_ddmarker: Remove bullets from list

Edit form coordinates preview had list bullets for each coordinate.

* boost: Prevent menu scrolling on quiz edit

* mod_quiz: Add bootstrap styles to edit quiz fields

Pagination and max grades forms.

* quiz: Undo some custom styles on review options

These checkboxes were laid out in a fake grid with no responsiveness
that conflicts with the bootstrap form-inline templates. Reset the
custom style to bootstrap default.

* quiz: Fix unit tests for boost changes

* qtype_ddwtos: Accurate positioning of drop targets

* questions: Make the review page responsive

* question: bootstrap 4 compatibility

.alert in bs4 contains no colours by default, you need to mix it with
one of the context classes to get some change in colours, borders etc.

Because Bootstrap Javascript does is not expecting to be flipped, it breaks the popover on RTL languages.
We already swap the directions on the help icon template so popover scss rules can be ignored.

This was present in bootstrapbase and is I think an important visual
distinction.

month is displayed in table caption which is by default in the bottom in BS4

Added a link to create a new message from the message
popup menu.

Remove existing overrides forcing the markup off

No idea what happened to my testing of this change, but it was wrong.

Bootstrap makes select form elements not using custom-select broken when
they have a size. The contents overflow the field.

Use a bootstrap popover for the assign roles form.

This just injects bootstrap classes into the old yui2 thing. It needs
rewriting.

The main change is that in boost we get rid of the random centered text.
To compensate we use "container" which is fixed with with auto margins -
but the text is still left aligned.

I stayed away from big markup changes. This is a table layout so needs rewriting which is a big job.

I removed most of the layout styles and started again.

Increased bottom padding to allow space for the lower edit menus to be
displayed without a vertical scrollbar.

They should be left aligned with a header, content and footer (right aligned with the buttons).

There should be a primary continue button and a secondary cancel button.

On the participants page, hide the small cog and put a region main
settings menu with all the nodes from the "Users" branch in the settings
block.

Update the HTML coming from the JS to include bootstrap classes.
Delete as many styles from boost scss as possible.
Regression test on clean and do final tweaks in less.

Grader report has custom overflow handling which does not cope with a
scrollable content region. So we need to make the content region flow
weirdly out to the right of the page, and push the blocks underneath -
even on really wide screens where it looks bad. We also needed to
upgrade the custom scroll code to handle the margin on the body
changing.

Fixes a problem where the drop down list is cut off by overflow.

Changing the display was messing with the layout of some things in the
file picker. Lets set the min-height instead which has less
side-effects.

We need to set a display value on the file picker body so the inline height is ignored.

Also fixed are problems with frozen select from elements showing raw
HTML. I checked the other form templates for similar problems and fixed
them all.

Add bootstrap classes to form fields and remove random centered text.

It was an unstyled list of links. This changes it to tabs with sub-headings.