use admin notices

admin notices are more common in wp
Merge pull request #34 from MaZderMind/warn_no_show

warn if no show is configured
add shortcode to list download links

- [podlove-episode-downloads]
- lists all available files as download links
- next up: whitelist for download links
minor changes
add podlove webplayer as submodule
update readme
remove readme fork link
auto-activate podlove web player
configurable web player formats
settings: improve button placement
add support for podlove web player
add Feedburner support
add chapters column to release table
add support for chapter marks
webplayer fixes
change media player hook

now our media player won't be loaded by podlove if it exists as a
standalone plugin
avoid possible crashbug
update webplayer submodule
fix: handle incomplete media_locations
add WordPress readme.txt