MDL-43347 grades: consistent interface for drop lowest setting
MDL-43347 grades: convert keep highest to text field
MDL-16474 scale: Allow scales with 1 item
MDL-42393 calendar: Preventing open/close loop in events overlay
MDL-46126 upgrade: fix bogus nulls in user.password before changing precission

Note: there is no need to deal with Oracle empty strings here
because only MySQL running in non-strict mode is affected.
MDL-43848 messages: do not display message content in popups

The user is not in control of when these popups show up and it
may not be appropiate to have part of this content display whilst
in the presence of other users.
MDL-43848 message: remove unused strings
MDL-45616 repositories: more clearly distinguish when we use source and when reference

Function repository::get_moodle_file() should always be called on packed reference and not on the source received from user.
Also added phpdocs to some other methods that were confusing source and reference
MDL-45616 repositories: use json encoding instead of serialization
MDL-45616 repositories: API changes to avoid serialized data in user input
MDL-45463 mod_lti: Prevent XML entity injections from provider
MDL-45417 mod_imscp: Prevent entity injections from package content
MDL-46148 qtype_calculated: unit tests + fixes for validation
MDL-46148 qtype_calculated: Remove unused function.
MDL-46148 qtype_calculated: function to validate equations in text.
MDL-46148 qtype_calculated: validate formulas everywhere.
MDL-45760 make sure to check permission before setting header
MDL-45683 user: Escaping Skype ID used in profile
Merge branch 'MDL-42393-master' of git://github.com/FMCorz/moodle
MDL-46042 badges: Clean up external badge data

Signed-off-by: Yuliya Bozhko <yuliya.bozhko@totaralms.com>