Add a visualization for process-incoming errors.
Add some more options

Add options to save the graph and data independently, as well as
an option to combine the current data with previous data (so that
we can keep a longer history than 24hr).
Fix baselines and interpolation
Add charts for specific error types.
Fix a variable name.
Remove some unneccessary dependencies.
Add argument offsets to format strings (for 2.6)
Refine "combine with old data" logic.
Cleanup index.html
Fix "combine with" logic, fix data timestamps.
Merge branch 'pi_error_viz'