Adding min, avg, max etc to column header tooltip
Removed padding attempt
Shows tooltips with statistics in the column headers

int, float and double: min, avg, max, sum
date: min, max
merged primary master (again) and resolved conflicts.
	Merge branch 'master' of http://github.com/Realm/realm-cocoa into gk-browser-minmaxavg-tooltips
Removed helper methods in accordance with JPs comments, restricted statistics computations to tables.

This is done because the min/max/avg methods are not supported for linkviews yet. It can be solved by lazily using get_sorted, but that seemed hacky.
Merge pull request #915 from GreatApe/gk-browser-minmaxavg-tooltips

Shows tooltips with statistics in the column headers