Allow specifying host images per texture

[Venomalia]

Fix #6 Allow specifying host images per hashed texture

[iwubcode]

Please rebase when you get time!

Also, how would you feel if you instead added the 'host controls' to a context menu instead? The button doesn't look horrible but if we decide to add more options in the future, it may be useful to already have a context menu.

[Venomalia]

with context menus I have my problems to set them up, I tried it but it just didn't want to. 😞
if you could help me there I would change it..

[Venomalia]

quick rebase.
I will try to add a context menu in the next days.