Place partition information percentages in their own column (#690542)

On some desktop environments, such as Unity on Ubuntu 13.04, the
partition information dialog can display the used/unused/unallocated
field values overlapping with the "(##%)" percentage value.  The problem
is pronounced for values with 4 digits to the left of the decimal (for
example a 1024 MiB partition ).  To address this problem, these
percentages are placed in their own column.

Bug 690542 - Partition Information Dialog Warning not readable