Merge tag '0.5.3' into develop

0.5.3 (2018-02-27)
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Features:

- Added admin interface for radios, track files, favorites and import requests (#80)
- Added basic instance stats on /about (#82)
- Search now unaccent letters for queries like "The Dø" or "Björk" yielding more results (#81)

Bugfixes:

- Always use username in sidebar (#89)
- Click event outside of player icons (#83)
- Fixed broken import because of missing transaction
- Now always load next radio track on last queue track ended (#87)
- Now exclude tracks without file from radio candidates (#88)
- skip to next track properly on 40X errors (#86)

Other:

- Switched to towncrier for changelog management and compilation