Rationalises the code for managing component loading

* Rather than individual compoments spawning their own threads to await the
  loading of the server manager, this provides a single
  ComponentLoadingManager singleton

* ComponentLoadingManager
 * Singleton that takes an implementation of the IManagedLoading interface
   as a callback as well as a set of Properties as arguments.
 * Manager awaits the restoring of the server manager then executes the
   callback on the same thread. It is up to the client callback to ensure
   they are running their code on the correct thread (especially if
   updating UI).

* OperationEditorPage
 * Must employ managed loading since it requires ModelerCore's query service
   which is sought from the runtime clients, thus requiring the server
   manager's default server version.

* PreviewModelObjectLabelProvider
 * Requires the use of ModelerCore's query service as well hence fitted
   with a managed loading.
Stop designer editors closing on startup

* Due to the moving around of the setting of the default server, editors
  are being closed on startup when the initial default server is set.

* Adds a flag to close editors only when restoring is absolutely finished
  and not just when the server manager is set to started.
Merge pull request #234 from phantomjinx/8.2.x

Fixes ....