Fixing some checkstyle issues.
allow to cancel world preview
add error label
ensure that only valid colors are generated
add progress percent to wait popup
Merge PR #1314 by @meniku - preview cancel option
Update readme - F1 clarification, two new modules, new contributor
parameter changes
Adding ImmutableBlockLocation for other classes to use, for example as a key in maps.
Merge remote-tracking branch 'upstream/develop' into develop

Conflicts:
	engine/src/main/java/org/terasology/utilities/concurrency/DynamicPriorityBlockingQueue.java
Merge pull request #1320 from MarcinSc/develop

Adding ImmutableBlockLocation for other classes to use, for example as a key in maps
Merge PR #1321 by @meniku - ladder improvements
Base classes for ObjectFacet3D, similar to ObjectFacet2D.
JavaDoc added.