mpr file fixes

[arndkoeppe]

Changes to process certain BioLogic mpr files that could not be processed before. To fix the issues below,

• Added an alternative technique param dtype for GCPL (0x77).
• The function param_from_key used to raise a ValueError if a single key was not understood. This is a drastic measure that interupts extraction of all successfully extracted parameters if one parameter is added. Replaced the error with a warning.
• Appending/merging multiple cycling files in eclab added an additional parameter to the settings, which caused the process to fail.

[PeterKraus]

Thanks for your contribution. Looks good in principle. Please let me know once the PR is ready for review.