Embed "Forward this conversation" input box in a form tag

Currently after entering E-Mail ID's in forward conversation input box if
you hit enter thread get updated rather than sending of E-Mail. So this
empty form tag is just to redirect enter to this send E-Mail button
Revert "Embed "Forward this conversation" input box in a form tag"

Nested <form> tags are against HTML specs so they shouldn't be used
This reverts commit b815d0cee98d92adf70811c8120d91c66fd31daa.
E-Mail coversation too if enter is pressed on input box
Case sensitive replace of instances of thread to ticket
Retaining post type as `sf_thread` for backward compatibility with older versions
Merge pull request #145 from VarunAgw/ticket

Rename "Thread" posts to "Ticket".

The `sf_thread` post type slug was retained for backwards compatibility.
Merge pull request #147 from VarunAgw/minor-changes

Process the Email Forward handler when `return` is pressed.

Previously there was a bug where hitting the enter key would submit the entire form, which would update the post rather than forward it.
Test attachment ID's if they are non-integer

Currently intval is currently an empty ID `` into `0`. Instead of this it
should be removed
Prevent locking in new thread

Currently it checks if E-Mail account associated with thread exists but in
new thread there is no E-Mail ID and thus E-Mail account associated with
it
Corrected coding standards