replace theme model with plain ruby object

register themes via configuration instead of creating them in database
migrations.

BREAKING CHANGE: the default theme has to be registered in the
pageflow initializer.
automatically register theme css files for precompile
theme generator

add a rails generator to copy the default theme into the main app for
modification
editing theming attributes through account admin

allow changing imprint/copyright link text/url of account's nested
default theming
ensure theming belongs to account

* associate theming with account on creation
* allow entry theming selection based on account name
fix column name in drop themes migration
new default theme based on fontawesome
further style fixes, local integration of fontawesome typo
added local entypo font, sass mixins for all font awesome icons
renamed fontawesome icon mixins
renamed all fontawesome icon classes used
sharp loading spinner
fixes scroll arrow sprite
logo graphics fixed, forced uppercase for title and tagline taken out of default theme
add assume method to quotas

can be overriden by quota classes to create new quotas from additional
assumptions.
add waiting_for_confirmation state to encoded files

* has to be enabled by configuration option
* confirm_encoding state machine event
add action_required file stage state

represent required user interaction for encoded files in
waiting_for_confirmation state.
count and notify about confirmable files
json endpoint for file encoding confirmation
begin confirm_encoding view