Allow setting the various LC_* env variables

Since there is only a very finite number of LC_* variables (LC_CTYPE,
LC_TIME, ...) we create class parameter corresponding to their LC_*
equivalents which can be set by the user and end up in
/etc/default/locale. All $lc_* parameters default to undef. This should
fix issue #13.
Merge pull request #14 from antaflos/manage_more_locale_vars

Allow setting the various LC_* env variables