Analysis should fail gracefully on missing trace data

[ptooley]

E.g for missing PAPI_TOT_INS:

• Analysis should gracefully fail with a warning about missing events and insert np.nan
• Reloading a summary with missing data should raise a (silenceable) warning of missing data
• Metric creation should silently accept nans in metric input
• Metric table plotting should support hide_nans={"never", "all", "any"} to control plotting of rows containing nans.