The 'from' time sample (i.e. the last smooth result
not later than the 'from' time) is included in the
range in which the 'zero' and 'max level difference'
instability conditions apply.

This patch also avoids a potential division by zero
(that would occur if the max- and min levels were not
found).

This covers the case where the user
unintentionally tries to compute the index or ASF stats
without having any filter values explicitly set.

To determine whether a result history is unstable for the ASF stats,
the tests for zero values and max-min difference are now
applied only to results that are within the from..to time range.

The result history details page now shows more relevant
information, like the 'from' and 'to' times, the actual
samples to be picked, and the outliers.