Major Overhaul (manual xml parser)

* killed feedparser since it’s not really usable and I reached its
limitations (multiple entities (of the same <entity>) would be
overwritten). now parsing xml manually with lxml

* add support for automatic author creation
* add support for categories
* add support for tags
* made language configurable
* fix text plugin language
* fix text plugin character encoding issues
* actually use the provided slug
* fix misleading log
* removed unused imports
* fixed some minor code issues (unclosed file pointers, obsolete code etc)
* pep8
use app_data for import information
missing requirements, organize imports, pep8
Merge pull request #6 from aldryn/feature/xml-parser

Custom XML Parsing instead of using feedparser