Refs #8906 - More descriptive names for monitor workspaces.

Essentially, the name of the original workspace name with a "_monitors"
suffix.
Refs #8906 - Move get_monitor method to Sample class.
Refs #8906 - SliceEvent now gets monitor from Sample class.
Refs #8906 - Cleaner way to load monitors for event files.
Refs #8906 - Use a scaled version of the same monitor.

Instead of passing the resulting monitor from SliceEvent to
NormalizeToMonitor, just use a scaled version of the same monitor that was
passed to SliceEvent.

These changes should also make the process of having monitors in a
different time regime easier, which is an issue we will be facing in the
future.
Refs #8906 - Only run scale when necessary.
Merge branch 'feature/8906_improve_monitor_handling_in_isis_sans' into release/3.1.x