UI locking fixes for GraphExplorer implementations

GraphExplorer implementations contained ExplorerState restore code that
was ran synchronously in the UI thread. It will possibly require DB read
transactions which locks the UI up. Persisted explorer state loading has
now been moved into a Job from GraphExplorer implementations and
GraphExplorerComposite.

Also contains fixes for doSetColumns of all graph explorer
implementations which was using a Map with the wrong keys.

gitlab #160

Change-Id: I879fe4a099db70d5d8bbba185b4dc9d745c80911