MDL-41359 database: no table columns is a dml_excpeiton

When insert_record is called and it doesn't find any columns
to insert data into, that is a dml_exception as you need at least
one column in the database to insert into it.  This can happen
when you have created a zero column database table, or the table
does not exist.
MDL-41292 cache: only update identifiers if they change
MDL-43074 assignfeedback_editpdf: Use escapeshellarg for all args in exec command.

This is to fix a reported problem with windows compatibility (e.g. when ghostscript is installed in
a folder with spaces in the name).
MDL-43025 EditPDF: Increase memory limit when reading source pdfs.
MDL-25473 mediaplayer - prevent embedded videos from looping
MDL-40920 mod_url: replaced add_to_log calls with events
MDL-43306 restore: fix grade item sortorder restoration

Previously, restore was blindly inserting the old sort order into the
database, causing duplicate sortorders which lead to unpredicatble
sorting results.

Now we will use the api function to add it after the original sortorder,
this means if a duplicate exists in the original location, this item
will appear after it.
MDL-43311 Repository: Added missing global CFG
MDL-39725 database: Add statistics collection functions
MDL-39725 database: Include stats collections in unit tests
MDL-39725 database: Apply database statistics update to daily stats
MDL-34321 Assignment2.2 - Fixing submission count
MDL-36984 Assign: Add redirect after saving grades
MDL-38832 course: remove unused constants
MDL-43355 testing: Return the hash when HEAD points to a hash
MDL-43268 fix filter notice when not in debug mode
MDL-43213 try to simplify behat config and init code

1/ always require 3 behat settings - $CFG->behat_wwwroot, $CFG->behat_dataroot and $CFG->behat_prefix
2/ cleanup init code
3/ do not require $CFG->wwwroot and $CFG->dataroot on test sites
4/ remove switch completely - the most confusing part for me
5/ print out behat_wwwwroot in init script so that you can test the test site manually
MDL-43235 behat: Ensure that behat_config_manager::get_config_file_contents() has always a behat_wwwroot
MDL-41075 Remove "Choose..." option from participants page.
Merge branch 'w51_MDL-43268_m27_filternotice' of https://github.com/skodak/moodle