Differentiating blocks, minerals and cooktime and 3 layers for ore generation

Blocks, minerals and cooktimes were the same for all ores (e.g. the mithril block has the same attributes as the silver one and thus was less tough than the diamondblock). Also the ore generation was not according to default (just one layer instead of three).

In more detail the changes are: 0. The upstream commit from OgelGames is applied.

1. For registering the block and mineral nodes the values can now respectively be added in the local oredef (there are also default values).
2. A cooktime for lump -> ingot is added (if not defined, this is set to 3 as default (not in the code here)).
3. Blocks, minerals and cooktimes for tin, silver and mithril are chosen differently. 3.1 The mithril block is probably now the first block with level=5 (> level 3) to result in a higher digging time and lower uses than for the diamondblock. It can only be dug with a mithril pickaxe. 3.2 Because of 3.1, all mithril tools have now max level=5. The digging times and uses are adjusted, so that they are still better for lower level blocks than the values for diamond tools (e.g. 315 versus 30 (or 40) uses for level=3). 3.3 The mithril block is now also TNT resistant.
4. There are now three layers for ore generation. Mithril appears now in clusters like the other ores (but is still less common).