Check if fixed to ICRF matrix is defined when computing approximate LVLH.
Merge branch 'master' into approximateLVLH
If computeFixedToIcrfMatrix returns undefined, use computeTemeToPseudoFixedMatrix.
DynamicPositionProperty falls back to computeTemeToPseudoFixedMatrix if computeIcrfToFixedMatrix fails due to lack of EOP data.
Modify convertToFixed to return a vector when computeIcrfToFixedMatrix returns undefined.
Make paths fallback to `computeTemeToPseudoFixedMatrix` as well.
Timeline destroy cleanup

1. Properly implement Timeline destroy to make sure everyting cleans up after itself
2. Add a sanity check spec that creates/destroys the Timeline as a stopgap until we write complete specs.
3. Fix a bug introduced in #870 that caused the Timeline to not redraw properly on scroll/zoom.

This change does not attempt to fix the myriad of other issues with the Timeline, so please don't review it with our normal rigor.  I'm hoping to carve out some time soon to finally get around to #754.
Merge pull request #874 from AnalyticalGraphicsInc/widgetCleanup

Timeline destroy cleanup
Completely disable the symbolSummary instead of just partially.
If beforeAll/afterAll fails, display an error.
BaseLayerPicker improvements.

1. Add ability for the BaseLayerPicker to have an item specify an array of imagery providers, instead of always using a single provider.
2. Added missing documentation to the ImageryProvider documentation.
3. Cleaned up the BaseLayerPicker code so that it only removes items originally added by the widget, rather than removing the layer at index 0.
Add a stack property to DeveloperError and RuntimeError.

This makes those errors display properly when thrown by specs.
Merge pull request #869 from AnalyticalGraphicsInc/approximateLVLH

Approximate LVLH
Fix errors when cleaning up the imageryLayer_reproject context cache object.
Fix destroy to release the shaderPrograms correctly.
Destroy the scene transitioner before destroying the scene.
Merge pull request #875 from AnalyticalGraphicsInc/baselayerpicker-multiple-providers

BaseLayerPicker improvements.
Merge pull request #876 from AnalyticalGraphicsInc/displayBeforeAllAfterAllErrors

Display errors thrown from beforeAll/afterAll
Merge remote-tracking branch 'origin/master' into dataSourceBrowser