Fix regression in buildModuleUrl.

A reference to `baseUrlString` was incorrectly changed to `baseUrl` by #1026.
Fix `JulianDate.fromDate` input validation.

Also remove a few old redunant specs.

JulianDate still needs a full clean-up pass at some point, but I resisted the urge to do any more for now.
Merge pull request #1033 from AnalyticalGraphicsInc/fixFromDate

Fix `JulianDate.fromDate` input validation.
Add min/max terrain level option to ImageryLayer.
Merge pull request #1036 from AnalyticalGraphicsInc/minMaxLevel

Add min/max terrain level option to ImageryLayer.