Fix regression in DataSourceCollection.removeAll.

Add spec to make sure that removeAll actually removes all data sources.  Fixes #1772
Merge pull request #1773 from AnalyticalGraphicsInc/fixDataSourceCollectionRemoveAll

Fix regression in DataSourceCollection.removeAll.
Test workarounds for IE 11
Improve reference doc for options parameters
Bump version.
Getter doc fix
Use memberof in defineProperties
Include VERSION property in Cesium object.
Remove memberof from functions
Put back comments for formatter
Remove more memberof on functions
Merge pull request #1779 from AnalyticalGraphicsInc/version

Include VERSION property in Cesium object.
Merge pull request #1776 from AnalyticalGraphicsInc/ie11-premultiplied

More test workarounds for IE 11
Merge pull request #1777 from AnalyticalGraphicsInc/options

Improve reference doc for options parameters
Merge pull request #1778 from AnalyticalGraphicsInc/type

Use type' instead' of 'return' for getters
Remove even more memberof from functions
Merge master to refdoc
Add Cesium.VERSION to CHANGES
Merge pull request #1780 from AnalyticalGraphicsInc/refdoc

Clean up memberof in reference doc
Doc cleanup.

Fix various typos and doc errors.