Differentiate minerals, blocks and lumps

[GreenDirkfried]

Both of the new ores have minerals, blocks and lumps with the same attributes. This does not make sense to me.

Minerals: use lower cracky group value for mithril, so that silver has
groups = {cracky = 2},
and mithril has
groups = {cracky = 1},

Blocks: the mithril block should have a higher level, so that for silver
groups = {cracky = 1, level = 2},
and for mithril
groups = {cracky = 1, level = 3},
or even
groups = {cracky = 0, level = 4},
adjusting the mithril pickaxe for the latter case.

Lumps: i suggest to change the cooktime for cooking mithril lumps to ingots as
cooktime = 5,
(default should be 3)

At the moment I don't now how to implement all of these changes. Probably one would have to add some if functions?

[GreenDirkfried]

Also at the moment the block has too much groups, it is
groups = {snappy = 1, bendy = 2, cracky = 1, melty = 2, level = 2},
instead of just
groups = {cracky = 1, level = 2},
For example, a consequence of the "snappy = 1" is that one can break a mithril block with a diamond sword, while this is not possible for a diamond block.

[GreenDirkfried]

Another idea to let the mithril block stand out would be if one makes it resistant to (TNT) explosions by adding
on_blast = function() end,
(This is done for example for the "tnt:boom" node in https://github.com/minetest/minetest_game/blob/master/mods/tnt/init.lua, as well as, similar for the maptools nodes.)

[GreenDirkfried]

#47