WMTS cleanup

This is some cleanup to some stuff I noticed while reviewing #2275.

1. The WMTS provider is always `ready`, so remove the uneeded if checks and variable.
2. Add spec for WMTS url generation code.
3. Add @relet as a contributor.
4. Update changes (which I forgot to mention in #2275).
Merge remote-tracking branch 'origin/master' into wmts-cleanup

Conflicts:
	CONTRIBUTORS.md
Merge pull request #2282 from AnalyticalGraphicsInc/wmts-cleanup

WebMapTileServiceImageryProvider cleanup