Changes to SST1MEventSource (#729)

* Add test using SST1MEventSource in the calibration pipeline

* Cleanup of SST1MEventSource

Removed functions inside containers
Corrected tels_with_data into a set
Added the channel dimension to r0.tel[i].waveform

* Corrected telid for subarray

* Added container to __all__

* Filled event_id and tels_with_data for other levels

* Moved TelescopeDescription so that it is not re-created for each event

* Add obs_id for the other data levels

* Some minor corrections

Restored relative import
Corrected comment