Add an in progress spinner that is suitable for the dark theme.

Add dark spinner to "Add New Show" (searching indexers), "Add existing shows" (Loading Folders), Coming Eps and all config pages (when saving).
Merge pull request #44 from SickragePVR/feature/AddDarkSpinner

Add an in progress spinner that is suitable for the dark theme.
Fix theme identification for spinner when restarting.
Merge pull request #45 from JackDandy/feature/FixRestartRef

Fix theme identification for spinner when restarting.