Added a class for the Measurememts Table that defines constants for the table and column names.
Fixing Measurement Controller so it returns correct data for all climate elements except precipitation. More work on the latter is needed but it is much simplified because the delta is now part of the data in the table.
Fixed the ClimateElementFactory as it did push an Climatelement to the array in default case.

Signed-off-by: Christian Rapp <0x2a@posteo.org>