CMFileManager: Improved confusing, cumbersome and incorrect strings

The string describing how you cannot move a folder to an invalid
destination seemed confusing and cumbersome. Here is my suggested edit.

Also fixed a minor typo in another string as well as cleaning up
reduntant error title string.

Change-Id: I7c94433a0a8c3d176e806038cfdac2d48a1f6432