Refs #8731. Disable Peak Picker tool when Fit Prop. browser deleted.

Otherwise need to do that manually in MuonAnalysis, which is very
error-prone.
Refs #8731. Minor refactoring.
Refs #8731. Toolbar hiding as signal.

We don't need it to be called instantly and this avoid the kinds of
problem we faced in a ticket. Things in hideEvent and showEvent should
ideally just emit queued signals.
Merge branch 'bugfix/8731_muon_fullscreen_freeze' into develop