Check permissions in frontend

Form fields are disabled using the new `{% input_editability %}`
template tag.

Other blocks are checked using the following `if`-statement:

    {% if 'tncapp.write_access' in perms %}

PS: Yes, `editability` *is* a word! https://en.wiktionary.org/wiki/editability
Added ConfigParser to settings.ini
Added settings.sample.ini
Updated Travis CI config

With the new split config file we need an additional configuration step
in .travis.yml.
Added TIME_ZONE to settings.ini

Refs tnc-ba/strongTNC#94.