Numeric Labels in Graph views

[nolanmar511]

Right now, only values associated with the "bytes" tag will ever be displayed in any call graph views.
This is because of the following section of code:
https://github.com/google/pprof/blob/master/internal/report/report.go#L244-L253

We should change how this works. For example, if there is no "bytes" tag for numeric data, we should use the first encountered numeric tag.

[nolanmar511]

Tag being displayed could be noted in legend as "nodelete tag" or something similar.