Splitter should be a lower z-index than errors

In fact, I’ve removed it since I have no idea why it would even need a higher z-index.
Load from the local cache, not file system
Remove defer redundancy
Trigger file update events on add/remove

* Renamed from `raml-source-updated` to `file-updated` to better reflect the actual event occurring. 
* No longer emits with the editor source, as that had awkward cross location file dependencies (source from editor and file path from the currently selected file)
* Trigger file update events when a file is created or removed (this should be changed, but I have no idea how we can properly track file !include dependencies right now)
Move file created event and add generated event
Fix test for loading !include
Load file from filesystem if not loaded already
Merge pull request #252 from mulesoft/raml-file-exists

Raml file exists