Gmail Herald full changelog

* New features:
* Added ability to manually iterate (back and forth) over the multiple messages in
* notification window
* Added ability to mark email messages as read from the notification window. This
* feature requires enabling IMAP support for Gmail account
* Added ability to check for application updates
* Extended tray icon with notification capabilities: show warnings and tool tips,
* Refactored version control code
* Change the application settings file location - now it stored in the user
* preferences system directory
* Bug fixes:
* Fixed notification window behavior: it does not freeze the whole GUI anymore
* Improved notification window layout
* Now changing application settings take effect immediately and not after restarting the application
* Fixed spelling errors in localization texts
* Multiple small fixes and improvements

1) Fixed wrong separators usage issue in GMail Herald executable path when save it into the Windows registry for starting the application on system start up. This prevented to GMail Herald start as expected. Now the native separators used instead.
2) Improved version control system.
3) Implemented