The Steinhart-Hart algorithm allows more precise thermistor
tables, but also requires more parameters, which aren't
available for all thermistors. Accordingly, add support for both,
the traditional logic using the beta parameter as well as the new
one.
This also adds thermistor-presets, so users can simply choose
from a pulldown-menu to set their thermistor.
Also, identical thermistors get merged into one table, saving
binary size.
Last not least, a few bugs in this area got fixed.
Usually, all these things go into separate commits, but they were
contributed all in one and separating them is a bit error-prone
for little gain.
This should address issue #130, #134 and #135.
jbernardis