Membership management - org page updates

[yumiendo]

• add 'members' tabs (introduce tabs for featured org pages...)
• update the actions below org description - "follow this organisation", "group message"(for org members only), "edit organisation info"(admin only)

...more to come.

[yumiendo]

Add/invite colleague

• after submit, show modal screen with confirmation https://cloud.githubusercontent.com/assets/8006323/16346537/d165a7bc-3a15-11e6-90f3-7a4665afe048.png

several possible cases:

1. if person is already HDX member > org admin(s) receives membership request (this is skipped if added by org admin - if there are multiple admins, they receive email confirming someone is added) > (otherwise) if admin approves > person is added to the organisation
2. if person is not registered on HDX > person receives email to register(email draft here - the link should go to the page below, assuming we can skip the verification process).
   > Once the registration is complete, admins receive membership request > User is added or rejected. (and person receives email confirming the role)