Checks for data completeness

[JakobBD]

Currently, incomplete data or string mismatches (such as typos in scenario names in the config, or technology names in the projects file) do not lead to errors, but instead to zero's in the data. This is dangerous behavior, as it is easily overlooked.

Some of the fillna's and merges should be adapted, such that missing data throws at least a warning, or even leads to a stop of program execution.