Tdf.extensionuploadcenter

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- Adding file extension validation for linked extension releases [Andreas Mantke]
- Adding image extension validation to project module [Andreas Mantke]
- Adding file extension validation to release module [Andreas Mantke]

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- Shorten boolean testing expressions [Andreas Mantke]
- CSS list style optimisation and style fixes [Andreas Mantke]
- PEP-8-Fixes [Andreas Mantke]

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- Adding a MANIFEST.in file [Andreas Mantke]

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- Updated the translation template file [Andreas Mantke]
- Added a missing closing div to the project view [Andreas Mantke]
- Added a validator for the release and linked release name uniqueness and it's adapters [Andreas Mantke]
- Changed the compatibility list in the project view to a text line [Andreas Mantke]
- Removed an obsolet div from the project view [Andreas Mantke]

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- Reordering of the project view template [Andreas Mantke]
- Removing the navtree from project and releases view [Andreas Mantke]
- Update of strings in the internationalisation template file (pot) [Andreas Mantke]

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- Add of README.md [Andreas Mantke]
- Removed doubled directory of tdf.extensionuploadcenter.egg-info [Andreas Mantke]