fix structure of disqus_static plugin and update README
Merge pull request #144 from idyedov/update_disqus_static

Fix structure of disqus_static plugin and update README
i18n_subsites: consider templates lang, expand docs

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.