Ability to build from different Style folders

* Added a "reference" folder which contains the default style
* Althernative folders can be added to the style folder
* Build system can be configured to use defined folder for style file.

- spec file currently only uses reference folder but will be configurable from build system in future

Change-Id: Ia24efc50112a03d0048d24665d0f5ce6b2b01c08