[FIX] Fix Incorrect texture path
[FIX] Fixed incorrect textue in FontMaterial when multi texure

• [NEW] Support Multi texture
• [CHANGE] Move plugin to Plugins directory

Disabled Rebuild on play mode

Fixed some bugs

• Display nothing when import a font in unity 5.5+ 

• Create the font without material when import a font in unity 5.4 

• Incorrect preferred height and alignment

• Cannot create the font if texture path has space