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

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.

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