Code inspection and fixes.  Remove unnecessary throws clauses and imports.
More inspections, removing warnings and other minor issues.
Replacing unclear values with constants.
Removed unused variables from old movement system.
Minor refactoring, removed redundant initializers.
Changed logInPlayer to use try-with-resources
Changed jar Message file extraction to use try-with-resources
Change writing of received World file to use try-with-resources.
Changed logOutPlayer and updatePlayer to use try-with-resources
Fixing typos, improving documentation.
Added position check to state change requests to prevent spoofing large jumps.
Formatting
Added comment about potential security risk, try-with-resources
Refactoroo
Improving documentation, analyzing code
Added World.xsd