Added Selecting Recipients functionality

Added new activity RecipientsActivity where user can select who the
media will be sent to.

There is a ListView with checkboxes that will display if the user has
friends. If not, they'll see a message that they need to add some
friends first.
I also must have hit the format key somewhere.

MainActivity now has an intent to start RecipientsActivity after a
successful result.

There is currently no send button, however.