Add support for named denominations.

This PR adds support for configurable named denominations, such as can be seen in this example config:

https://github.com/elBukkit/MagicPlugin/blob/master/src/main/resources/examples/potter/Gringotts/config.yml#L15

The configuration is backwards compatible (I've left the default alone) and supports a mixture of simple and complex denomination configurations.

The list can also contain a mix of named and unnamed denominations, as seen here:

![PotterGringotts](https://lh4.googleusercontent.com/-EOuXN4WWJKI/U5c9prIICAI/AAAAAAAAAbU/WRwE-xGuRL8/w714-h171-no/GringottsHP.png)

The "galleons" (emeralds) stored in the emerald blocks still count, though they are not displayed as blocks. The lowest denomination will still use the formatting string to output the remainder, and will be used for a 0 balance (meaning the lowest denomination should probably be named!)

I've also tested this with the default config and it still works as expected.