Continue without sound if OpenAL setup fails
Don't setup player instance in headless mode
Fix & streamline the gradlew startServer config.cfg generation - second JSON pass was overwriting the first pass
Remove duplicate OpenAL library loading and add logging
Replace switch with only one case with if statement
Fixed warnings in asset package
Merge pull request #1071 from msteiger/fix_221

Continue without sound if OpenAL setup fails
Fixed most of the warnings in audio package

* Mostly trivial changes
* Roughly 100 warnings in total
* Mostly raw type warnings
* Missing override
* Hide inherited field (playing)
* Some casts were necessary
* And several per-method template names
* Covariant return types were used where appropriate
Split NetworkMode.SERVER into LISTEN_SERVER and DEDICATED_SERVER

Most follow-up changes are rather straight-forward
Added NetworkMode to NetworkSystem to be able to decide which mode to
enter.
Use StaticSound for sounds and StreamingSound for music assets
Made BaseSoundSource fields private
Added Static/StreamingSound to serialization libs
Removed BaseSoundSource playing member
Tiny tweaks - log statement, move "crouch" to "CTRL", rename binding descriptions for crouch and jump slightly
Use boolean flag to indicate NetworkSystem host mode
Fix type names with underscores
Merge pull request #1072 from msteiger/fix_1069

Don't setup player instance in headless mode
Make AssetData conversions in AssetManager more explicit
Fix checkstyle type name warning
Remove client entity from relevance region when removed