Extract functionality for submitting collected data

Kai Koehne requested to merge kkoehne/kuserfeedback:data_submitter into master
  1. Added "interface" AbstractDataSubmitter which is the base class for all data sending strategies.
  2. Added "interface" AbstractJsonDataSubmitter which is the base class for all JSON sending strategies.
  3. Existing data sending functionality is extracted to the DefaultDataSubmitter class.
  4. Simplified existing solution: used built-in redirects resolving instead of manually implemented.
  5. Qt 5.9 is required.

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