Image Tracking support added

I added Image Tracking support!

The plugin sends Image Library from Editor to remote device on every scene launch so you don't have to make a new build every time when your Image Library is updated.

ScheduleAddImageJob is also supported in Editor.  Please ensure that a texture is readable (set Read/Write Enable in Import Settings or create your texture in runtime) before calling this method.

The easiest way to test Image Tracking is to point your device at your computer screen with opened image. Also a great way to save paper :)