Show players that signed themselves up as reserve for concurrent battles

See feature request #9
Link to battle history against clans in battle schedule

See issue #7
Show replay duration in battle details
Avoid listing an enemy clan multiple times for encounters in schedule
Battle schedule bugfix
Download link for replay archive of filtered battles

Archive download is memory intensive for now, as the archive is built
in memory. To be rewritten later to use the file system.

Also hide download link in battle details if replay does not exist.

Hiding the download link fixes #12
Archive download is a feature request in #1
Hide archive download link if no battles shown
Add link to add battle to battle group page

The appropriate battle group will be preselected.

Warn if uploaded replays are missing the "pickle" part, i.e. where the
battle duration cannot be determined automatically and which cannot be
used in player performance calculation

Link from battle groups was a feature request in #1
Merge branch 'master' into feature/fame-points