Stats panel: Make formats more flexible.

* Adds capability to change the formatting individually for modes.
  E.g. 'count' shouldn't be displayed in bytes, rather it should just
  be a natural number.
* Implementation: define individual formatting functions for each mode
  and patch up the angular template as needed.
* (Closes #1285.)

Signed-off-by: Joe MacMahon <joe.macmahon@cern.ch>