Context menu: reword "Add to new container" action

[abey79]

For a single item: "Wrap in new container"
For multiple items: "Move items to new container"

[abey79]

Both of the copy above tend to be on the verbose side. In #5392, the copy changed to "Move to new container" (for both single and multi-selection). @nikolausWest ok for you? I can do "Wrap to new container" for a single selection, but I think it'd be kind of weird to have a very different term used for mostly the same thing.

[nikolausWest]

Fine by me (at least until we come up with something better 😛)