Added support for Icedove
Fixed bug #56: Toolbar icon wasn't displaying properly in Firefox+Linux. (Still need to test on other platforms.)
Removed debug code that was forcibly re-adding button to Firefox toolbar on every run
Firefox: Added disabled style for toolbar button that grayscales it. (I believe that this is only necessary on Linux.)
Altered grayscaling of disabled button to leave a little colour (not fully desaturated)
Created grayscale-ish images for the disabled toolbar button rather than using the svg trick
Prepping for release
Merge branch 'development'