Fix Translations in Form Fields

Form fields in Mezzanine generally use `ugettext`. This induce problems in `accounts.forms` and `generic.forms` since some forms in these modules have "static" fields. Using `ugettext` on static fields causes the translations depend on the language when the module is first loaded, rather than dynamically depending on the current request's language setting. I switch to use `ugettext_lazy` on those fields so that the translation behaviour can be correct.

I checked the other apps too, but they don't seem to they have no static form fields. Not entirely sure whether I missed anything though.