GriefPreventionFlags

• Adds guards against bad or missing YML data in messages.yml, flags.yml, and clusters.yml. Gives a nice error message instead of a stack trace.
  
• Expands '/gpflags reload' to include all YML files.
  
• Adds command '/gpflags compactdb'
  
• - Removes erroneous claim ID's (happens automatically also)
  
• - Removes claim data for claims that do not exist (happens automatically also)
  
• - Removes messages, trust lists, and flag values for flags that do not exist.
  
• - Removes flag data for flags that are the same as the global value.
  
• - Removes claim entries that have no flags set.
  
• '/setmessage', '/getmessage', and '/removemessage' are now '/setflagmessage', '/getflagmessage', and '/removeflagmessage' to eliminate alias conflicts with '/gamemode'. Old commands still work, but not the old aliases.
  
• Tested with 1.6.1 and 1.6.2 developer builds and messaging abilities of a player flag

- none