Remove default mod

flare-engine now supports loading the default mod from either an
installed copy of flare-engine, or from a local folder like
`~/.local/share/flare/default/mods/`.
Merge remote-tracking branch 'upstream/master' into fixes
Merge pull request #320 from stefanbeller/credits

Splitting up credits for mods.
Merge pull request #313 from dorkster/fixes

Remove default mod
Chinese by lonsine
change speeds to tiles per second
adapt melee_range to a tile unit
adapt thread_range to tile units
change autopickup_range and powers range to tile based units
change radius of powers to tile based