give each service a unique name
filter services by name
new social filter API

- “type” param renamed to “category”
- new “type” param to filter by service
- adjust core templates to match new API
- add migrations so table columns match API wording
- rename internal method names to match column renaming
doc update: one flattr is enough
remove unused method
build backend and API for tracking

- move tracking/redirect/download code from shortcode.php to plugin.php
- add 2 models: DownloadIntent and UserAgent
- add url accessor which can be given source and context
use public file URLs for templates and player
add text index to user agent string
add filter to bypass DNT-header

Only for debugging, of course.
update readme
merge
merge
fix notices
fix ADN manual announcement episode list
list ADN episodes by time
search now covers episode fields
update readme: mention tracking
when redirecting, keep ptm parameters
templates: add sortability to podcast.contributors

fixes #391
templates: option to limit published contribs

fixes #392