hideHeader misplacement bug fixed
Performance improvement
Merge branch 'hideHeaderBug' of https://github.com/mathiasdose/ng-grid into mathiasdose-hideHeaderBug

Conflicts:
	src/js/core/factories/GridOptions.js
fix(Header): Hidden header height misplacement

A hidden header caused the scrollbar and viewport to be drawn lower and
smaller than they should have been.

Fixes #1995

BREAKING CHANGE: The `hideHeader` option has been changed to `showHeader`

To migrate, change your code from the following:

`hideHeader: true`

To:

`showHeader: false`
fix(Pinning): Add left border for right container

There was a border on the left container but not on the right container;
no visual separation.