If you're logged in as a client, stay that way

When following a link from an email, if you are already signed in to the
help desk as a client, you should just be redirected to the new ticket.
Only ticket owners can update ticket details
Pre fill user email address on sign-in page
Add more emphasis to the subject line
Merge pull request #948 from greezybacon/feature/client-ux-tweaks

Several small tweaks to the client user experience

Reviewed-By: Peter Rotich <peter@osticket.com>