Fixed issue #9

[ENHANCEMENT] Colored the messages of /rssetprices.
[CHANGE] Changed syntax of /rssetprices. Optional store argument is now first. Together with this I also re-wrote the execute() command with a better syntax check and so on.
[BUGFIX] Fixed players with the right permissions not being able to manage admin stores.
[BUGFIX] Fixed console not being able to use the /rssetprices command.
[BUGFIX] Corrected wrong help text (and also changed the usage text to one easier to understand).