Add validation of load profiles

Asserts that:

  * The file does not use CR (\r) line endings. Such files will not load
    correctly in the Merit library (and aren't "correct" on any modern
    platform anyway).

  * That the values in the load profile won't overload or underload the
    producer in the Merit Library.
Merge pull request #840 from quintel/load-profile-validation

Add validation of load profiles