String for unified collection view tooltip

[Téo Mrnjavac]

Hello
I've noticed that the tooltip for the toggle unified collection view
ToolButton says "Toggle unified view mode. This is an experimental
feature". I have briefly discussed it with Lydia and we're not sure
that the "experimental" part is appropriate for 2.2 final.
Unfortunately the string has already been translated but fortunately
it shouldn't be a big change in most languages to remove the
"experimental" part.
Max, do you really want to keep the whole string in 2.2 final?
If not, please remember to email the translators when you remove the
second sentence.
Cheers
Téo