Added the `RequestLog` Model to the possible exports

Added `gzip`, `tgz (tar.gz)` and `tbz (tar.bz2)` to compression methods for exporting
Added mime-types for the contents to the response.

Changed rendering in an abstraction method `_render_json`,
to implement further render methods for `protobuf` or other similar structured datatypes.
Merge branch 'develop' into export-requestlog
Missed the changes in the template to use new exports.
Merged the changes from the `adhocracy.hhu_theme`.
Merge branch 'develop' into export-requestlog
Removed the "csv" option from the formencode, the code responsible to handle this option is thrown out, due to nested dict structure of the export data, that the "csv" format not easily could represent.
fix whitespace in proposal meta links
[scss] split overwrite
[scss] split utilities
[scss] split grid
[scss] split font
[scss] split html5
[scss] split bootstrap
[scss] split forms
[scss] split type
[scss] split morelink
[scss] split showmore
[scss] split tooltip
[scss] split badge
[scss] split button
[scss] split modals