[Contacts list] Send invites by email to enroll new users

[giomfo]

• Add at the top of the contacts list the following item (see design page v4):
  

Tapping on this item opens a new screen used to invite individually some people via their email address.
The design is available in page v1:

• This screen list all the local contacts who are not Tchap user yet. We may consider first only the local contact with an email address. We will consider the contact edition later (if need). If a contact has several email addresses, please duplicate the contact to keep one email by contact (= row).
• At the top a search input is available to search in this list
• a multi selection is supported, as soon as a contact is selected, the option "Inviter" is enabled at the top right in the toolbar
• if the user presses the "Inviter" option, we invite individually each selected email by creating a direct chat (see tchap v1). We have to talk about this method before reporting it in tchap v2. Please read the tchap-ios implementation here, note tchap-ios doesn't support multi selection (only one email at once)
• Below this search input, an item (button) is displayed:
  
• Tapping on this item opens a dialog used to fill one or more email addresses to invite (see tchap v1)
• in all cases, a notification (a toast) is displayed for each email to provide a feedback (failure/success/other) to the user

[giomfo]

replaced with #86