Implementation of sources for csv files + several bugfixes

[johanneshiry]

Resolves #101
Resolves #103

New features

• Initial implementation of CsvRawGridSource
• Initial implementation of CsvDataSource
• Initial implementation of CsvTypeSource

Fixes + adaptions:

• CsvFileConnector now converts camel case field names to snake case to account for database field names
• adds a missing field in ConnectorInput in the InputDatamodelConcept.puml documentation
• renamed field noOfParallelDevices to parallelDevices (+ adapted documentation + tests accordingly)
• removed TimeTools from Processors as they cause a lot of trouble in several places and replaced them with default ZonedDateTime.toString() (=harmonising ZonedDateTime handling for I/O operations in processors + factories)
• fixes a new bug in AssetInputFactoryInput introduced by Extractor for nested Models into their own collections for persistence  #78
• fixes a bug in EntityProcessor that lead to processing of the internal node of a three winding transformer + adapted tests accordingly
• fixes a bug in EntityProcessor that processed parallel devices in SwitchInput (which defaults to 1 and has no constructor field -> should not be written out) + adapted tests accordingly
• adapted DataSink interface -> removed getConnector() + added shutdown() and persistSubGrid()
• added electric vehicles to SystemParticipants class
• added method to DataSink to persist a JointGrid directly
• added method in ValidationUtils to determine if a collection of UniqueEntity elements contains distinct uuids or not + corresponding test

[codecov]

Codecov Report

Merging #102 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #102   +/-   ##
=========================================
  Coverage     71.35%   71.35%           
  Complexity     1264     1264           
=========================================
  Files           198      198           
  Lines          4856     4856           
  Branches        537      537           
=========================================
  Hits           3465     3465           
  Misses         1090     1090           
  Partials        301      301           

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