Fix bugs in ComponentsEntityCollection

1. `onCollectionChanged` handling was not properly resetting a value to undefine for each iteration of a for loop, leading to the first entity incorrectly being the target for all merged properties.
2. Fix bug in `Entity.merge` which was causing custom properties registered on the source entity to not propagate to the target entity if they did not already exist.
3. Added specs to expose both issues.

Fixes #2180
Don't use `+` for space in `objectToQuery`.

Apparently some ArcGIS servers are non-spec-compliant and don't properly handle `+` as space.

Fixes #2192
Add comment about the workaround.
Merge pull request #2193 from AnalyticalGraphicsInc/objectToQueryWorkaround

Don't use `+` for space in `objectToQuery`.
Merge pull request #2185 from AnalyticalGraphicsInc/composite-fixes

Fix bugs in CompositeEntityCollection