Actually fix the config-reset bug.

Some of the config-file resets were fixed in a previous commit:
4330885d469dd3f0e71676527d05f061785344aa

The resets fixed previously were ones where snakeyaml would throw a fit
due to tabs. Because an exception is thrown, the call to saveConfig()
is never reached, which means the config-file is never reset.

However, errors resulting from other illegal characters were not caught
because the built-in reloadConfig() method catches, prints and then
simply does nothing about any exceptions thrown, which means the actual
YamlConfiguration would be empty. Saving this empty file would result
in a reset, because MobArena, during initialization, sees missing bits
and pieces and tries to insert them. Thus, the resets were not an issue
with MobArena's attempt to keep the config-file tidy, but the reckless
handling of errors in the built-in config methods in JavaPlugin.

This commit completely overrides the methods in JavaPlugin that would
result in these resets, and the MobArena plugin class stores its own
reference to the config file and an associated FileConfiguration. When
the reloadConfig() and saveConfig() methods are called, the checked
exceptions are caught and rethrown as unchecked exceptions, causing the
plugin to crash when it needs to do so.