Mass-replaced colour with color in po/

For conformity's sake. As a british person, this pains me.
Changed instances of colour to color in .py files

See #155.

A codebase should read like it's been written by a single person, and
spelling differences like colour/color impact that. Consistency is key.
Fix permissions on .glade file

Doesn't need to be exectutable
Proper templating for gettext strings w/ >2 "%"es

Addresses translation warnings seen in #156.
Translation README.md: update contact email

Also some minor stylistic and typo fixes.
Fix build for translation=*

Closes #156.
Merge branch 'colour-to-color'