Fill table with values from preferences.

git-svn-id: https://mcomix.svn.sourceforge.net/svnroot/mcomix@799 6cf541bf-b722-4a7c-9fc0-fb1e75421f59
Fill 'Open with' edit window with some functionality.

Add/Remove/Preview are working, Save still requires input
validation before allowing the user to actually save.

git-svn-id: https://mcomix.svn.sourceforge.net/svnroot/mcomix@800 6cf541bf-b722-4a7c-9fc0-fb1e75421f59