Implement "View full-screen"

* Event wiring for "View full-screen" button.  Though the event
handler is in place, registration of the click event for this button
has been disabled mainly because once in "full screen mode"
there is no way to navigate back to the drops view/listing
Generate CSRF token once per session

* Regenerating the token during each time token validation
is performed causes DOS. E.g. A user being unable to use
separate browser tabs for form submission
Implement sharing dialog

* Implemented the dialog for sharing drops. Twitter and Facebook
sharing are still performed as before i.e. a pop up window loads
the login page for the selected service before the user can proceed
with sharing

* For email sharing, the share dialog transitions to "email sharing" mode
where the user enters the CAPTCHA and recipient's email address.
Stubs for drop comments API resources