provide user-friendly unit downloader based on MaStRAPI

[gplssm]

Remaining todos

• Move unit data download (for now only "eeg") to separate function
• Test additional unit data download
• Add additional unit data download (kwk, permit)
• Flatten returned dictionaries
• Convert data to appropriate types
• Join to single table
• Review CSV saving with column naming and data type specification of soap_api/
• Apply duplicate elimination as done in soap_api/
• Fix encoding when saving to CSV
• Compare column names per file with old/new downloader