MDL-38555 forms: Prevent same data submission multiple times.

This disables Submit button when the form has been submitted to
prevent consequent submissions before the page has been loaded.
MDL-32898 Final deprecation of moodle_strtolower()
 MDL-34508 Formslib: Removed deprecated setHelpButton() from editor.php and hidden.php
MDL-33379 course: Removed deprecated move_section() from course/lib.php
MDL-35666 remove uninstall protocol option
MDL-39454 Accesslib: is_siteadmin is a bit slow
MDL-39449 course view.php: don't require forum lib.php

As far as I can see, it is not used, except in social course format, so
I moved the include there.
MDL-39490 Inform the developer about incorrect order of text processing

Before calling format_text(), the text must be processed with
file_rewrite_pluginfile_urls(). This order is important
for some text filters that look for valid pluginfile.php URLs.
MDL-39472 MUC: Optimise cache::get_from_persist_cache
MDL-39155 Quiz: Provide 3 image-size options on the settings page
MDL-38019 Log filter enable/disable
MDL-38019 added add_to_config_log() to lib/datalib.php
MDL-39608 - Bootstrap - Chaning the thresholds and width values for the Form labels
MDL-39629 theme_formal_white: added support for new admin_setting_configstoredfile setting element
MDL-39489 behat: Updating to 2.6 moodlehq/behat-extension tag
MDL-39639 Formslib: Hide calendar for datetime element on disable event
MDL-28558 Administration: Made Country and City user profile fields optional
MDL-30320 question engine: remove API deprectaed in Moodle 2.2.
MDL-39227 - SCORM - repositioning the navigation panel to be visible in all themes at all resolutions
MDL-39947 mod_forum: Add safety check to variable assignment when counting unread posts