Improve usability for storefile stats in web status pages

Right now the "Storefiles" section of the Region Servers status shown in the Master web ui is inconsistent in units (sometimes "m" and sometimes "mb") and uses units that are fixed rather than adapting to the number being presented (e.g. reporting a bloom filter size of 13540k instead of 13m).

Clean up to

• consistently use correct units (i.e. KiB, MiB, GiB since that's what we're measuring)
• adapt the units used so that we use the biggest ones