Support deleting dictionary configurations

* Deletes from list in Manager dialog.
* Deletes XML file from disk.
* Current implementation does not attempt to differentiate between
  shipped templates, and user-created configurations.
* Current implementation just uses a Yes/No messagebox rather than
  a dialog with a Delete button.
* Part of LT-15468.

Change-Id: I5caa18b48193fdf879922c83fd6a91d3b09fbfc9