Use gettext for plugin translation

[rimas-kudelis]

This translates the widget using gettext, however, the language setting doesn't seem to work, needs some more digging or to be removed entirely.

I changed language codes because WP doesn't seem to be smart enough to fallback to lt when it can't find lt_LT.

Fixes #33.

[rimas-kudelis]

Okay, so the switcher works, but there's a gotcha: the switch_to_locale() WordPress function will only switch locale if it deems that that target locale is installed/enabled.

For example, I can only switch between lt_LT and en_US on my installation.

@ovx, how much do you want to keep that setting? I'm thinking maybe it's not that useful when the language is properly selected automatically?

Also, WP requires .mo files for the translation to work. I committed them to the repo, but I'm sure it's also possible to generate them before pushing the plugin to WordPress SVN instead.

[ovx]

@rimas-kudelis Hi, thank you a lot for this PR, gettext was definitely planned. I think the language settings can be dropped since it works automatically now. Will review this a bit later.

[rimas-kudelis]

Cool, in that case I've updated the plugin to remove that setting.

I kept some code, which should still make it possible to switch to a specific language when using the shortcode, but I didn't test that scenario.

By the way, do you even ensure that altcha is correctly submitted if it was inserted via the shortcode?

[rimas-kudelis]

By the way, originally, the array of 'en' translations contained the following extra string:

"cannot_submit" => "Cannot submit."

I coudn't find this identifier in JS, meaning the seems to have been unused, so I have removed it.

[rimas-kudelis]

Marked more strings for localization.