Add Globe.baseColor

Allows for setting the color of the globe when no imagery is available.
Minor Sandcastle fixes
Merge pull request #2151 from AnalyticalGraphicsInc/fixes

Minor Sandcastle fixes
Changes after review

1. Add unit tests for changing base color.
2. Make sure new properties are initialized in the constructor.
Merge pull request #2149 from AnalyticalGraphicsInc/globe-color

Add Globe.baseColor
Minor tweaks to Geocoder

This prevents the Geocoder widget from both allowing editing of text while searching and also prevents submitting of the text "Searching..." while already geocoding.

Fixes #2087
Fix widget error handling

Fix #2095 by making sure that exceptions generated by onTick callbacks are handled by the widget.
Remove superflous messaging from errors that are most likely not WebGL related.
Merge pull request #2153 from AnalyticalGraphicsInc/geocoder-searching

Minor tweaks to Geocoder
Merge pull request #2154 from AnalyticalGraphicsInc/ontick-errors

Fix widget error handling
`foreachLoadedTile` should not enumerate tiles in the START state.

Such tiles aren't "really" loaded.
Update CHANGES.md.
Add a spec for forEachLoadedTile change.
Merge pull request #2155 from AnalyticalGraphicsInc/forEachLoadedTile

Fix a bug in `QuadtreePrimitive.forEachLoadedTile`
Lighter theme for NavigationHelpButton added
Added import for the new css
Merge pull request #2159 from macoda/master

Lighter theme for NavigationHelpButton
Clamp tilt to [-pi / 2, pi/ 2] and add Camera.roll.
Merge branch 'master' into tilt

Conflicts:
	CHANGES.md