Fix for issue #19

This sets locale to "C" before reading and writing banks, and resets it to environment settings afterwards.

When reading saved files, it also tests, if the value is an integer, then it loads the value using environment locale, so older banks can be read as well:

`0,700000` will be read as `0` on first try, and on second try, it will be read as `0.700000` if the locale has `,` as decimal separator.