MDL-44364 theme_bootstrapbase: Clean up calendar variables

There are a few reasons why I am cleaning up the calendar.less file.

1/ The variables were too specific, and unlikely to be overridden. If
   you are going to change the colour of the background, surely you will
   change the border to match the background. And if you want to do
   more advanced things, you will override the selectors anyway.

2/ If you wanted to re-use the color of the event, but not as a
   background or border, you would have to use a variable that
   was specific to the background or the border, a generic
   variable for the event colour seems required.

3/ The colour @redDarker should not be defined there, and its purpose
   is so limited that I do not think we need it at all. Also,
   this variable is unlikely to be re-used ever, better not
   introducing it.

4/ I removed the calendarHeadingsColor because those headings should
   really match the rest of the headings throughout the site. I
   removed it from the overlay, but used the standard Bootstrap
   one for the one in the page.

There are still a few things that would need improvement, like the
usage of @white for the background of the event, which will not really
look good on a dark background.
MDL-44597 lessphp: Add sourceMap support in theme designer mode
Merge branch 'w13_MDL-44661_m27_anon' of git://github.com/skodak/moodle
MDL-44670 themes: Updated screenshots of Clean and More
MDL-44590 category: correct get_string component
MDL-44590 behat: Add test for course category idnumber duplication
Merge branch 'w13_MDL-44639_m27_taskdocs' of git://github.com/skodak/moodle
MDL-43681 report_log: Modified log report to use log readers
MDl-43681 report_log: Added Behat test for report log
MDL-43681 logging: Invalid events are not added to get_events_select

If event is not restored then don't add it to returned list of
events in get_events_select
Merge branch 'wip-mdl-43681' of git://github.com/rajeshtaneja/moodle
MDL-28261 Javascript: Check for a working connection in SCORM activities
MDL-34353 Javascript: Allow chooser dialogues to fall back to non-JS version

In order for a chooser dialogue to be able to fall back to it's non-JS
equivalent, we need to use a different set of styles.

This change makes the chooser dialogue preparation function add a new class
to the body which is utilised in the CSS to accomplish this. When the class
is not present, the dialogue content is displayed inline.
Merge branch 'MDL-44357-master-noplugin' of git://github.com/FMCorz/moodle
Merge branch 'w13_MDL-44511_m27_jquery' of https://github.com/skodak/moodle
MDL-43960 assign: Add missing include

There was a report of mod_assign_save_grade webservice failing because of this.
I couldn't reproduce it, but grepping the code found one place where this include
should be added.
Merge branch 'MDL-44535-master-v2' of https://github.com/jamiepratt/moodle
MDL-43839 unit test fixes
Merge branch 'MDL-44075-master-v3' of git://github.com/jamiepratt/moodle
MDL-44739 theme_more: Set default theme settings