Don't wait for slow imagery before rendering a tile.

As long as the imagery's parent tile is available, we can use that instead
of waiting.  This lets us show faster imagery sooner rather than waiting
for the slowest imagery attached to a tile.
Add a note for myself for later.
Refactor imagery loading.

This fixes the crash that previously occurred in this branch when zooming
in past the available imagery, and makes the code much less insane.

At this point performance appears to be outstanding, but memory usage is
higher than before.  I'm not sure why yet.
Fix layer manipulation.
Remove debug code and unused property.
Proxy/server fixes.

* Avoid null pointer exception when proxy URL has no host.
* Add better MIME types for several file extensions.
Fix test failures.
Load json in a beforeAll so it only runs when the specs run.
Avoid use of real, resolvable hosts in tests.

such as "fake.net" and "up.com".  Instead use the ".invalid" TLD which is reserved.
Merge remote-tracking branch 'origin/master' into noWait
Update CHANGES.md.
Fix typo in build file.
Merge pull request #849 from AnalyticalGraphicsInc/fixProxy

Proxy/server fixes.
Merge pull request #850 from AnalyticalGraphicsInc/fixHostsInSpecs

Avoid use of real, resolvable hosts in tests.
Merge pull request #851 from AnalyticalGraphicsInc/noWait

Don't wait for all imagery attached to a tile to be loaded before rendering the tile
Merge remote-tracking branch 'origin/master' into tileEdgeArtifacts