Improvements to support internationalisation

[th3-z]

Completes issue #1 with the following new features.

• Locale selection
• Translation templates and setup.py commands to update them
• Compiled catalogues are generated during build automatically

I've added the currency symbol ($) and code (usd) to the translation templates, only one's supported by the API will work. I have also refactored the main script a bit because it was getting long.

The relevant commands for managing the templates are:

python3 setup.py extract_messages - Pulls all the target strings out of the codebase to produce pot file

python3 setup.py update_catalogs - Updates the generated po files, use when strings change

python3 setup.py compile_catalogs - Compiles just the translation files, yields mo files

Additionally python3 setup.py build will now compile translations and copy them into the build.

[Yakonche]

Nice work, thanks for your help !