Allow an ignore list on constructing SpectrumDetectorMapping.

Enables filtering of given IDs when the list is first constructed.
Refs #7890
Fix spectrum numbering for ISIS event files.

Uses new ignore id feature on SpectrumDetectorMapping and also
sets the spectrum numbers on the resized EventWorkspace to those from
the file.
The default numbering scheme of starting at 1 is not sufficient as
a monitor block may be start of the table.
Refs #7890
Merge branch 'bugfix/7890_isis_event_monitors' into develop