Add basic block events

Add license headers
Fix LiquidSpreadEvent
And re-add renamed file...
Merge branch 'master' of https://github.com/SpongePowered/SpongeAPI into blockevents
Merge remote-tracking branch 'origin/blockevents' into blockevents
Add block break causes

Add license headers
Merge branch 'blockevents', remote-tracking branch 'upstream/master' into blockevents
Add more block causes, move things, fix Javadoc...

Add license headers
Merge branch 'blockevents', remote-tracking branch 'upstream/master' into blockevents
Rewrite block cause system to be more extensible
Merge branch 'blockevents', remote-tracking branch 'upstream/master' into blockevents
Make Cause a class, add new Reason, move things
Extend CauseTracked
Merge branch 'blockevents', remote-tracking branch 'upstream/master' into blockevents
Merge branch 'blockevents', remote-tracking branch 'upstream/master' into blockevents
Add BlockBurnEvent, BlockIgniteEvent, BlockChangeEvent

Add license headers
Merge branch 'blockevents', remote-tracking branch 'upstream/master' into blockevents
Add SignChangeEvent and fix some bugs
Add EntityPerformEvent
Rename EntityEvent to BulkEntityEvent and EntityPerformEvent to EntityEvent