shell: Disable chunk size for RAID 1

Disable the selectpicker for RAID 1
Show the text "0 KB" for RAID 1
Set the chunk size to 0 when creating RAID devices

Fixes #1071
This is digging into the implementation details of the selectpicker.  We shouldn't do that.  Let's just disable #create-raid-chunk and make sure to pass 0 to the D-Bus call.