Make recalculation of fluoro high dose data asynchronous

[David Platten]

The recalculation of summed DAP and RP dose data when updating high dose alert settings can take a long time (15+minutes). This would greatly benefit from being done asynchronously using the run_in_background method, as is the case when the home page summary is populated (populate_summary in views_admin.py).

The method that takes a long time is rf_recalculate_accum_doses in the views_admin.py file. The method is called from the highdosemetricalertsettings_form.html when a user clicks on the Recalculate all summed data button.