resourceloader: Consistent stylesheet order for debug and non-debug

Previously, style modules were only in a predictable order for production mode.
In debug mode, the order was determined by order in which modules were added
to queue at run time. This made it sometimes hard to debug, especially when
dealing with gadgets that apply in a different order among each other.

Change-Id: I4bff0c91d127e4ad8015cd8c1775220fe460cbc3