VSTheme: Added sharedTheme convenience method.
VSTheme: Added -(NSShadow*)shadowForKey: method.
Refactored all VSThemeLoader code into VSTheme class methods. This mades possible subclassing VSTheme and using the singleton pattern.
Fixed subclassing issue.
Introduce -hasKey: method to check if key exists at all

Conflicts:
	Source/VSTheme.h
	Source/VSTheme.m
Updated podspec to OE repo