+ remove "Preview unavailable" and only set preview as invisible if no video device
+ fix preview not starting after branching device
+ resets eudiometer if no videodevice.listsize changes
+ fix preview visibility in recorderbox
+ fix recorderbox closing when changing from conversation to settings

GitLab: #608
GitLab: #610
Change-Id: Ie7069934abdf5005ed8360fad20c0de20bdc1a43