Set 'reply_to' in all emails and fix target language in some

Also fixed the locale used to send webconf invites to use the receiver's
language.

cherry-pick 172324e8229e4e1bfee0687a9e2f2322bc79eecd
Solving conflicts on:
	app/controllers/locale_controller_module.rb
Can't use an invalid email in "Reply-To" header

Some mail services will fail to deliver the emails if the Reply-To header
is set to "reply-to" since it is not a valid email.
This was true for Amazon's SES.

cherry-pick c0e6f20107b1e763ed11ee831136e73c61d48040
Fix emails being sent with the wrong mail address, fix #713

All emails have to be sent with the email configured in the Site. Spams
and feedbacks were being sent with the email of the user that created the
spam/feedback. This fails for some SMTP servers and is wrong.

cherry-pick 1696f298e8a025df552ab63e55ee3a76abd4651f
Make sure all rooms have passwords when created

A room without password can cause errors when it is updated in case it is
private. Better have passwords all the time.

Partially adapted from f6e6bf5d6bd3f4f0ca951fb5d6af70b10b25e273
Fix the language used to send emails (in the new version), refs #670

cherry-pick 32a75a5238f8d6d0ae3fa8c9d88612816a0a854b with adaptations
Fixed some translate problems in InvitesController

cherry-pick 1056d319b91263d06a2b6a6844258482a434717b