Support constructors for PlayScript scalar classes

This isn't true constructor support, instead it converts expressions
like:

	var num:Number = new Number(1.0);

to:

	var num:Number = 1.0;

This resolves issue #140.
Fix NumberIsFloat handling of properties
Workaround code generation bug (AOT?) with default null string.
  Default string that was set to null is actually set as empty string
  at runtime.
Added caching to getDefinitionByName().
Make the NumberIsFloat attribute work w/ interfaces
Merge branch 'master' of https://github.com/playscript/playscript-mono into dj-rad-fixes