[Code Cleanup]
* [CHD-3257] [Mail/Parser] Mail with a subject line comprised entirely of whitespace will have the subject rewritten as '(no subject)'.  This makes it easier to click and modify the tickets in worklists.
* [CHD-3217] [Usability] Fixed an issue with the auto-grow text boxes where OS-level keyboard shortcuts no longer worked if they involved PgUp, PgDown, Home, End, or the arrow keys.
* [CHD-3217] [Mail/Preferences] Added an option to worker preferences to control the initial size of the reply text box.  The auto-grow functionality of the text box can also be disabled as a preference.
* [Virtual Attendants/Mail] The generic 'Send Email' action in Virtual Attendants may now specify a 'From:' address. Previously, this action always used the default reply-to address.
* [CHD-3216] [Virtual Attendants/Mail] The 'Send Email' Virtual Attendant action is now capable of using placeholders to determine the proper 'From:' address.  For instance, on ticket behaviors it can use the current ticket's group and bucket to determine which address to use.
6.2.3 checkpoint
Merge branch '6.2.3' into stable