Database setup

[timonmerk]

Hey @SamedVossberg,

I am closing #330 and instead open the database work-package here:

• write nm_db.py module which creates sqlite table in outpath if it doesn't exists
• add sqlite write function nm_db.write_features after feature computation in run method
• remove feature_dict list aggregation
• add function in nm_db.py to write head of database as csv file and option to read back database as pandas dataframe
• return value of run method is pandas dataframe read from the sqlite database
• replace nm_analysis read of database as dataframe instead csv file
• check options with @toni-neurosc to load sqlite database in real-time into browser visualization