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.

Checking external_format_text return instead of just using SITE->summary

If we have the nofications and messaging popovers displaying on the
policy confirmation screen we hit an exception since the webservices
won't work if the policy hasn't been agreed to.

This patch simply stops them from showing if the site policy hasn't
been agreed to.

Thanks to Peter Klinka for the solution!

* Quick grading: Properly recognize unchanged grades
* Individual grading: Amend JS that transfers checkbox state

Must completely suppress notice from iconv as Behat's
shutdown function uses error_get_last() which is
unable to detect if the error was suppressed or not.

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

From bs4-compat.less, replace with file level disable instead.