Use Towny to restrict lava placement, instead of ranks

[MilesBHuff]

The purpose of disabling lava placement for those below the rank of Settler is to prevent griefing. However, one of the negative side-effects of this, is it makes it impossible for players to place lava dispensers, which have uses in industry.

One way I can think of to let us have our cake and eat it too, is to use Towny to disable lava placement outside of towns, and then allow people to place lava in plots they own.

We would have to test this to ensure that it is not possible to dispense lava into a Towny plot from outside the town. For those who remember: this is the incident that led to Settlers MC (the precursor to SettleScape) dying. I believe this exploit has since been patched in Towny; nevertheless, it's still something we need to test.

[MilesBHuff]

May be doable at the same time as #174.