Allow some customization from Launcher3

This patch allows a user to customize:
- Grid with and height
- Default homescreen position
- Visibility of the search bar

These items can be configured in a new Activity, which replaces the
system
settings as target of the icon in overview mode.

Shortcomings:
- Bounds for cols, rows and defaultWorkspace may need to be adjusted
- When one of the values changes, the Launcher activity gets recreated
completely.
- When searchbar is hidden, you also lose the visible hints for the
remove/appInfo drop targets.

org:
https://github.com/CyanogenMod/android_packages_apps_Launcher3/commit/32d479cfa98b7264271c79830789855dbfa94dcd