wip: runs code check on all existing editors when omni is toggled to ready
ensuring error messages get displayed for all files (before fix each file would clear previous file's messages)
code checks files on load.  Removes errors from error view on editor destroy.  Adds a new event  to atomsharper (atom-sharper-editor-destroyed|onEditorDestroyed) that other features can subscribe to if they're interested in when c# editors are destroyed.
remove editor reference once it is destroyed to avoid confusing which editor to draw in