[FIX] website_crm: 2 fixes commit, yeah

- admin is not follower anymore of all leads created through the
contact form. The famous no_subscribe key is added in the context
for that purpose.
- fixed medium and sales_team of the contact form leads. A bad
xml_id + bad use of get_object_reference + bad use of try/catch
prevented from having any of those. It now works correctly
even if the medium and/or sales team has been deleted.

Courtesy of Use Merge: Yannick Tivisse.
Reviewed by Use Merge: Thibault Delavallée.

I think this commit message is waaaay longer than the commit
itself, although I think I will never beat Olivier or
Martin. Those two are able to write 3 pages of commit messages
when doing a one-line fix. Well, this fix can be tricky
to understand but, hey, I am not writing stupid things just to
gain some characters. Not my style.

Have a good day.