OSB-44: adapted the backend of the station monitor to receive and display the wincc statuses - renamed payload to data

I made sure that if a time span contains observation with different mode but with modes regarding the same 
component the results are still returned for both. Additionally, a certain mode may not be for a long period.
So givin a mode a, it can happen that a certain component in the RTSM is not tested and result as green. This
a long standing issue. To solve this issue the RTSM should provide the mode in which the observation is perfomed. However, to mitigate the issue I am now excluding all the observations that do not have errors in a specific mode but have errors in another mode. This can still include spurious errors if such observation does not presents any RTSM error! ('luckly' it is very rare).

OSB-34: Setup of the preliminary implementation of the celery infrastructure, integration with the already existring django infrastructure and modification of the models to include and serve the RTSM plots

OSB-32: added additional filter field in the api requests to select the error types and url generation for the RTSM plots

OSB-28: add ordering by date and change in the summary parameters to include a lookback time instead of a datetime

OSB-28: Removed the RTSMObservationSummary model and modified the RTSMObservation to include a summary of the RTSM