[#3582165]Move udisks extension point insertion at beginning of fm_init().

Udisks extension point should be initialized before any other monitoring
operations because GIO initializes it only once and otherwise GIO already
have it initialized to internal one and will ignore our extension.
[#3588183]Be more verbose when show question about deleting files.

We should show either file name if it is single file or number of files
to delete so user will not accidentally remove wrong files.