Add prompt to open in TTV when importing from a different spec *directly* into current loadout

[alkerzor]

I just discovered you have detection for trying to import a loadout from a different spec (prompting to open in TTV)! Aaand it throws an error if you try to import anyway. Makes sense, though it'd be nice if this allowed just importing the class tree. That's how I discovered this, in testing for #41

It doesn't prompt if you try to import into the current loadout rather than saving as a new loadout, just gives you an error. This could probably still give the TTV prompt.

(I would assume this issue belong in the TLM repo, but ... mumptions.)

[Numynum]

If memory serves, the code doing this actually lives in TTV (TLM reuses blizzard's error popup, and TTV hooks into that)
should be fairly simple to do I think, but I'll just confirm that before actually moving the issue to the other repo 🙂