Use headless env. for testing
Increased class-level javadoc, renamed some launch argument variables, now handling command-line usage requests.
Readme tweaks and tiny javadoc addition
Wrapped launch arguments handling and exception logging into their own methods. Now taking advantage of the AutoCloseable feature implemented by the TerasologyEngine class, resulting in a more compact main method and a full handling/logging of all exception-triggering paths.
Merge PR #1397 by @msteiger - headless unit testing fix
Added /? as a print usage request flag, added missing argument to complete Usage string.
Add liquid data for water placed with Perlin. Explicitly set water's prefab.
Add null check so that items with null icons do not crash the client.
Merge PR #1396 by @emanuele3d - PC facade tweaks
Merge PR #1400 by @Josharias - prevent crashes from rendering held null icons
Fix ColumnLayout unit tests