[TIMOB-3115] iOS: Added memory warning event to Ti.App module
[TIMOB-3115] iOS: Documentation on memory warning event
[TIMOB-3115] Bump version of "memorywarning" event
Merge pull request #5490 from pec1985/timob-3115-3_2_x

[TIMOB-3115] Memory warning global event. Backport for 3.2.x