Disable the donate button on mobile platforms

The Google Play Store and Apple App Store aggressive policies to get a cut of sales mean that an included donation button may cause issues.

Merge remote-tracking branch 'origin/master' into 1.5-rel

Remove notarize release build for macos for now

Update Changelog (supertuxkart#5199)

* Update CHANGELOG

* Update CHANGELOG again

Create 1.4 release

Release 1.4-rc1

Update replay files version

Create 1.3-rc1 branch

Switch public ratings to a compound of raw score and RD

The raw score remain used in the core of the formula for expected scores computations.

Also improve the handling of disconnects on rating, with new RD floors
(and so public rating penalty) for recurring disconnects (>= 3 in the last 64 races).
The raw score is less penalized than before, as it's not needed and
make expected score computations more reliable.