Fix private message text for webconf invitations, refs #1020

Wasn't sending the message written by the user when sending the invitation
via private message. Via email was sending it correctly.
Fix wrong message in space invitation emails, refs #984

Was sending the message in the wrong language in some cases, and in some cases
using more than one language in the same email.
This was in the email sent to the admins of a space confirming that a user
accepted or rejected an invitation to join the space.
Remove option to invite people to spaces via email only

It doesn't behave properly and it's not a feature worth reimplemeting right
now. Invitations to join spaces now can only be sent to users that are
registered on Mconf-Web.

Only removed the fields from the invitation form, everything else is still
there.
Fix error introduced by 4c8ac733, refs #973

4c8ac733 checked for nil values before cloning the variables, but the call
to clone was duplicated right after it, and could cause errors.
Merge remote-tracking branch 'upstream/master'
Change the logic of who can record meetings

For spaces only members can record. For personal rooms, only the owner can
record. Superusers can record any meeting and anonymous users cannot record
anything.