Clarify Lz in docs

Lz must exceed maximum ice thickness.
No need for temp. storage in IceModel::putTempAtDepth().

Also: re-use a variable.
Move PS_EISMINTII from stc/eismint to src/coupler.

This makes it easier to re-use some code.
Reduce code duplication.

Move common code from PS_EISMINTII and PSVerification into PSFormulas.
Merge branch 'dev' into fevor
A bit of cleanup.