Fix the fix for bug 4346: http://bugzilla.lyx.org/show_bug.cgi?id=4346.

Fix the fix for bug 4346: http://bugzilla.lyx.org/show_bug.cgi?id=4346.
Synchronizing insets asserts with two views open

This finishes the change of http://www.lyx.org/trac/changeset/28587.

Replace the setButtonLabels functions that need a BufferView by buttonLabel functions. These functions modify the label at drawing time.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@28610 a592a061-630c-0410-9148-cb99ea01b6c8