BEER workflow and docs fixes

[jokasimr]

There are a number of improvements we should make to the Beer workflows:

• tc should be better documented in the place where it is set in the loader. The name should probably change altogether to make it more clear what it represents.
• We might be able to replace the chopper_delay_from_mode providers by using the lambda parameter from the McStas simulations.
• The difference between L0 and Ltotal should be better documented.
• The loaded data should have a position coord, to make the 3D detector view work.
• We should bin the data by pixel after loading to make the processing of the simulated data more similar to the processing of data from real files.
• Replace the referenced url to the NPI_tof_dhkl_detector McStas component with https://www.mcstas.org/download/components/current/contrib/NPI_tof_dhkl_detector.comp.