Fast livesync of images

[tzraikov]

Will sync all image assets in fast time (under 1 sec). This means sync for all the operations -add/update/delete.

[vchimev]

Currently in version 2.5:

• sync of images in <project>/app/App_Resources requires full rebuild of the native Android/iOS project and they sync in a couple of seconds.
• sync of images in <project>/app/ but not in App_Resources does NOT require full rebuild of the native Android/iOS project and they sync in a moment.