General Fixes

Config.yml:
It doesn't really matter what the baseRank is, but the ranks need to
begin at 1 and they must increment by 1 (not 10)

Plugin.yml:
The command tag (and all of its subsets) cannot be commented

PlayerManager.java:
Removed Referrences to PlayerManager
Added Comments where helpful
getRank(String) method now available

ConfigManager.java:
Added if-statements for to handle potential null-pointer issues
Changed numRanks() calculation from counting demotions to counting
promotions. (no particular reason)

EntityDeathListener.java:
Changed Frontier-class-variable name back to master (consistency)
Modified onPlayerDeath(EntityDeathEvent) to utilize SQL and Config
rather than the new PlayerManager class

LoginListener.java:
Removed references to PlayerManager. (Plus, code like what was there
should be going in the Frontier.welcome(Player) method anyway)