Initial port of JS canvas bindings to use QV4::Object subclass instead of V8 resources

Initial port of JS canvas bindings to use QV4::Object subclass instead of V8 resources

This patch comes with the same prototype injection as during the QML locale
patch. This will allow for incremental porting method by method for this huge
binding.

Change-Id: Ie258f021ac6f926302bb375a8ce7a12fb5e0512a
Reviewed-by: Lars Knoll <lars.knoll@digia.com>