Trebuchet: Hotseat fixes

This change fixes some of the bugs of HotSeat on landscape mode:
* Fixed distance algorithm for XY spatial (not only for X axis)
* Fixed cellX and cellY database handling when items are added in landscape mode
* Fixed cellX and cellY transtions when add new items
* Restore the current hotseat page on rotation

TODO:
- When a folder is removed because doesn't have more items, the last item
of the folder is saved at 0,0 (vertical) and drawn in the position of the
removed folder (creating a invalid small icon over the same icon)

Change-Id: I8b0faa5b6fde42d80e0d98226fca07eead04223c
JIRA: CYAN-315
Issue: https://jira.cyanogenmod.org/browse/CYAN-315
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>

Conflicts:

	src/com/cyanogenmod/trebuchet/Launcher.java
	src/com/cyanogenmod/trebuchet/LauncherModel.java
	src/com/cyanogenmod/trebuchet/Workspace.java
Trebuchet: Centers vertically the wallpaper

Actually, the wallpaper is not center vertically (both, with wallpaperhack and
without wallpaperhack). This patch modifies:

* Replaces the WallpaperOffsetInterpolator class by the Launcher2 implementation.
* Fixes mWallpaperHack. onDraw now centers the y vertically.
* Disable mWallpaperHack when there is only one homescreen (otherwise a black screen is displayed).

Change-Id: Ia5e0763c9a31609db8f7826f619ed808041e97e7
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>

Conflicts:

	src/com/cyanogenmod/trebuchet/Workspace.java

Signed-off-by: igio90 <giovanni.rocca.90@gmail.com>