MDL-32249 completion: Make grade criteria more consistent

Also, round course grades and remove hardcoded string.

Note: This patch also removes the ability to update the course grade
from the completion interface
MDL-33987_M23 theme_anomaly: amended some css values to style dock better also removed exclude parent theme stylesheet as it refered to a none existant file in base theme.
MDL-34019 Fix response item key name
MDL-32062 question engine: fix re-grading attempts from 2.0

The code to upgrade attempts from before Moodle 2.0 to 2.1 created
attempt data that was not exactly the same as a new attempt created in
2.1+. This did not matter very much - revew and the quiz reports all
worked OK - but it broke on re-grade.

These changes detect the problem data in the re-grade code, an apply a
work-around so that the re-grade gives the correct result.
MDL-30883 question flags: aria attributes for accessibility

Also, update code to use html_writer, and fix pointer style when not
editable.
MDL-33780 question import: strip UTF8 BOM

Previously, if there was a byte-order mark at the start of the file, the
import would just break, which was silly. Much better to just strip it
off.
MDL-34008 formslib: repeat_elements replace {no} for submits & buttons
MDL-33453 Make it clear what search_references() and search_references_count() are good for

Initially it was not clear enough that these two methods are supposed to
be used for looking for references to a stored_file only. So the docs
comments are improved and unittests added to illustrate the usage.

The patch also removes the unittest for get_references_by_storedfile()
as its usage is already covered in other test methods.
MDL-34044 completion: Fix regression caused by MDL-26626
MDL-32605 calendar: Fixing the missing parameter for get_string call
MDL-34025 - quiz secure window: fix popup closing
MDL-33924 quiz: incorrect foreign key definition.

Thanks to Jean-Michel Vedrine for spotting this.≈
MDL-31802: Remove section summaries from navigation_cache
MDL-34077 Repositories: Flickr and Picasa can have custom names
MDL-34096 Installation : Added 2.3 upgrade line to db upgrade scripts.
MDL-32297 Forms: Date Picker JS popup is not constraint to parent form
MDL-34119_M23 theme_splash: removed redundant js call in lib.php. Added lang option to config.php + amended lang output in layout files. Added some css to style langmenu + removed redundant loginicon in pagelayout.css
MDL-34045 fix invalid idnumber field type in cohort form
MDL-34115 fix sorting in blocks admin UI

Comparison of arrays is not locale aware.
MDL-33876 skip deleted users in enrol_database sync