this commit removes the need to make a dummy translation for
the language in which the templates are written.
This only affects themes using jinja2.ext.i18n.
The I18N_THEMES_LANG is introduced to address this issue.
Also expanded the docs for making gettext .po files with babel.
This plugin extends the translations functionality by creating i8n-ized
sub-sites for the default site.
This commit implements the basic generation functionality.