Improvements to IntegerRangeMapping, most notably support for "empty" (or 0-sized) range (these which only take a single value and use 0 bits to "virtually" read/write it).

TODO: make IntegerColumn support such empty ranges, and then let ChoiceField and MultiListField use such a potentially empty column
Added missing column to TRANSMISSION_PART_SCHEMA + fixed parts record query

Signed-off-by: Matthias Stevens <matthias.stevens@gmail.com>
Merge branch 'master' of github.com:ExCiteS/Sapelli