gnu: teeworlds: Update to 0.7.0 [fixes CVE-2018-18541].

* gnu/packages/games.scm (teeworlds): Update to 0.7.0.
[source]: Switch to git-fetch. Remove all bundled libraries except md5.
[arguments]: Adjust accordingly.
[inputs]: Use sdl2 instead of sdl and python-wrapper instead of python-2.
Add json-parser and pnglite.
* gnu/packages/patches/teeworlds-use-latest-wavpack.patch: Update it.