Fixed delete button

[Croden]

Hardcoded "delete/" link leads to 404 - changed this to be same as "submit_line" from django itself.

[coveralls]

Coverage remained the same at 82.688% when pulling 860ea24 on Croden:patch-1 into e181a1b on divio:release/3.4.x.

[czpython]

Hello @Croden,
Thank you very much for this contribution.
I've been quite busy this week, but will definitely review your pr no later than the weekend.

[czpython]

Hello @Croden,
Which django version are you using?

[haricot]

It works with django 1.8 and django-cms 3.4 but not with django 1.9 and 1.10

[haricot]

Just an example to quickly show what happens on this issue when we try to delete an extension object:

Page not found (404)
Request Method: GET
The current URL, /fr/admin/project/iconextension/15/change/delete/, didn't match any of these.

This URL should be :

/fr/admin/project/iconextension/iconextension/15/delete/

[czpython]

Thanks for the clarification @haricot.
And thanks to @Croden for the patch :)

[coveralls]

Coverage remained the same at 82.688% when pulling 860ea24 on Croden:patch-1 into e181a1b on divio:release/3.4.x.

[czpython]

Merged in d90102f