Fix sorting by value in details panel

[PapiCapi]

Hello, one of my players informed me that the Details panel wasn't sorting anything when selecting the "value" sort.

It seems that this issue is because :

• in the BlockConfig, now, most of my blocks are lowercase and are added this way in the map "blockValues".
• in DetailsPanel, when sorting by value, you were getting in the map with Material (o1.key() and o2.key() are Material) instead of a String.

As a result, I :

• ensured that the blocks added to the blockValues map are lowercase (because some in my config are also uppercase)
• converted the Material into a String and forced it to be lowercase because Material.toString() outputs an uppercase String.

Feel free to modify my PR as you like :)

[tastybento]

Thanks!