Complete new approach: download all values from new site to a file (.csv) and read values from the file.
Graph related changes.
Text annotation changes.
Updated OxyPlot.
Changed default URL. Removed old feed-reader. Added last date to graph text annotation.
Merge branch 'feature/historical_data' into develop

* feature/historical_data:
  Changed default URL. Removed old feed-reader. Added last date to graph text annotation.
  Updated OxyPlot.
  Text annotation changes.
  Graph related changes.
  Complete new approach: download all values from new site to a file (.csv) and read values from the file.