Settings new dashboard - part 2

Introduce the new Dashboard (a grid like presentation of
Settings top categories) per UX specification.

- the Dashboard is composed of "categories" and in each of them
you have "tiles"
- implement a new layout for showing top categories
(DashboardContainerView). This layout basically acts like a
grid
- depending on the device configuration make the grid with 1
column in portrait / 2 colums in landscape (phones) OR 2 columns
in portrait and 3 in landscape (tablets)
- take care of Accounts adding and removing (as it changes the
number of tiles to show)

Also remove all the old code related to Headers

Change-Id: Ie29944132c1b4c3f7b073d5a7d4453b8f5ec19a7