New release - 0.2.8

A new release of 0.2.8 is available with the following major changes:

* Directories window warns if no ROM or MAME executable chosen

* Add new filter group Status, filters Correct and Best Available, and add ROM availability filter buttons (SF Feature Request 2474989)

* Fix crash when removing last MAME executable directory in Directories window, prompt user if no executable or ROM path is set when closing the Directories window

* Fix segfault on startup if there is no .gmameui directory (SF Bug 2738775)

* If no MAME executables are defined when starting, user is prompted to open the Directories window

* When switching to a different MAME executable, prompt to rebuild the gamelist

* Added Swedish (sv) translation (thanks Daniel Nylander) (SF Feature Request 2544027)

* Code cleanups