Refactor out final uses of blocking dialogs

Replaces gtk_dialog_run() with equivalent non-blocking behaviour for the following files:

• eel-stock-dialogs
• nautilus-location-entry
• nautilus-file-operations
• nautilus-mime-actions
  • Partially complete, need to refactor activate_files

Opening now to get some feedback since the changes are more involved.

There is a bug with location-entry where the dialog is displayed twice, however this is also present in master.

I'm not sure how to go about porting mime-actions->activate_files(). I can think of either:

• breaking it up into methods which are chained together, or
• making the entire thing async and invoking a dialog on the main thread as we can then block on it.

Part of #1992 (closed)