Add language preference UI

[ibboard]

Now that ​ibboard:#30 has completed to improve the translation API and we're getting more languages through #203 it would be useful if we had some way of changing preferences other than editing the preference file manually.

This will require:

• A UI to set the value
• A refresh of the translated text
• Saving the value

[ibboard]

(In r535) Re #265: Add language preference UI

• Add initial preferences dialog with translation options
• Re-translate main form when language changes
• Save translation for later use

Only known bug on initial quick implementation is that open unit dialogs become named "{0}" (which should be replaced by unit name), but this should be quite a simple fix

[ibboard]

Some other translations are also not working at the moment: preferences menu item and label next to combo box. May just be typo in name and missing cascade option.

[ibboard]

(In r538) Re #265: Add language preference UI

• Make unit form and army tree translate on translation language change

Army tree title translation still seems patchy

[ibboard]

r537 should actually have been against this ticket as well

[ibboard]

(In r539) Re #265: Add language preference UI

• Fix army tree translating
• Make translations change on list change, not just on "okay"

[ibboard]

(In r540) Fixes #265: Add language preference UI

• Make unit equipment lines refresh when language changes

[ibboard]

Release as part of v0.1b8