generator: put a vein into each stratum, new view mode (H)

Known bug: some veins can be seen out in open. Reason is errosion destroys material, but can't destroy items (which vein nodes are). This is force-shut atm by forbidding veins in earth. New view mode - NO_BLOCK, press/release H.

Signed-off-by: mkhropov <mkhropov@gmail.com>
Merge branch 'master' of https://github.com/mkhropov/Elem