Adding a reInitSlidesArray method for extensions that generate new slides in the "beforeInit" phase
add an alert when reInitSlidesArray is used too late (after beforeInit)
fix possible double call to "beforeInitEvent.done()"

now surrounding beforeInitEvent notification with lockInit/releaseInit:
 - done() will be called as before (but with removed duplicate logic)
 - done() will not risk of being called twice (this happened when a beforeInitEvent trigger was locking and releasing the event fast)
Merge remote-tracking branch 'twitwi-mainstream/add-reinit-slides-array'
Merge remote-tracking branch 'twitwi-mainstream/fix-double-call-to-beforeInitEvent-done'
[anim] added header
[clone] updated header
[fit] updated header
[smartsyntax] updated header
[step] updated header
[svg] updated header