MRG: Refactor _TimeViewer slider representation (#7623)
MRG: Refactor _TimeViewer slider representation (#7623)

* Refactor orientation, smoothing, time and playback

* Refactor scale

* Refactor colorbar

* Refactor slider linking

* Improve viewers synchronization
drammock/mne-python,drammock/mne-python,Eric89GXL/mne-python,larsoner/mne-python,kingjr/mne-python,bloyl/mne-python,pravsripad/mne-python,olafhauk/mne-python,olafhauk/mne-python,olafhauk/mne-python,mne-tools/mne-python,cjayb/mne-python,rkmaddox/mne-python,Teekuningas/mne-python,bloyl/mne-python,larsoner/mne-python,wmvanvliet/mne-python,rkmaddox/mne-python,drammock/mne-python,wmvanvliet/mne-python,mne-tools/mne-python,wmvanvliet/mne-python,Teekuningas/mne-python,cjayb/mne-python,pravsripad/mne-python,kambysese/mne-python,Eric89GXL/mne-python,pravsripad/mne-python,kingjr/mne-python,larsoner/mne-python,kambysese/mne-python,Teekuningas/mne-python,kingjr/mne-python,mne-tools/mne-python