Add option to swap the Trash and Delete keybindings (allow direct
deletion with Delete key only)

Also update potfile
Update makepot to read .glade files, rename .ui to .glade, set translation
domain in relevant source files for gtk builder
Remove .po files
Merge pull request #223 from mtwebster/keybindings

Add option to swap the Trash and Delete keybindings (allow direct deletion with Del key only