Add a plant system for both double and single block plants

Valid plant names are Allium, AzureBluet, BlueOrchid, BrownMushroom,
Dandelion, DeadBush, DoubleTallgrass, Fern, LargeFern, Lilac,
OrangeTulip, OxeyeDaisy, Peony, PinkTulip, Poppy, RedMushroom, RedTulip,
RoseBush, Sunflower, Tallgrass and WhiteTulip. Those names can be found
in the comments of the BiomeConfig file. Plant names are case
insensitive. (Material names are now case insensitive too.)

Both the resources Grass and Plant now use the plant names. Don't worry,
blockId[:Data] still works too.

There is now a problem with the Grass resource. Because of the plant
names block data is no longer really needed in the Grass  and Plant
resources. Grass is the only resource that had a separate parameter for
block data (all others use block{:data]). That parameter is now unused.
We can't remove it, otherwise old Grass resources aren't parsed
correctly.

Some options to handle this without breaking old configs:

- create a new resource, remove Grass, automatically rewrite old Grass
resources.
- remove Grass, automatically rewrite it to Plant (note: the resources
aren't entirely compatible, Plant is also less efficient than Grass).
- let the second parameter do something else. We can't use it for
something numeric (then we wouldn't know if it was a block data or the
new numeric parameter), but we can for example let it be "Grouped" or
"Random" or something like that.