Home menu improvements

I've reworked the homemenu because I've had a couple of problems (couldn't enable the Addons in the music menu for example). Anyway I saw that you have the same problem I had when I was working on my mod. You have most menu buttons listed twice with a visible condition based on backspacehome.enable but this isn't really necessary because instead of setting a boolean value you can just save the "return" in a string and feed that to the ActivateWindow function:
```xml
<onclick>ActivateWindow(Videos,MovieTitles,$INFO[Skin.String(backspacehome)])</onclick>
```

And in the SkinSettings.xml:
```xml
<onclick condition="Skin.String(backspacehome,return)">Skin.SetString(backspacehome,)</onclick>
<onclick condition="!Skin.String(backspacehome,return)">Skin.SetString(backspacehome, return)</onclick>
<selected>Skin.String(backspacehome,return)</selected>
```

This allows for a much cleaner HomeSubMenu.xml and prevents bugs because you only have to write code once. There were a lot of menu entries that didn't have the return parameter at all or were hardcoded so I've added the same $INFO tag to them to provide some consistency. This has been tested with pretty much every menu entry except the live TV ones because I don't have the PVR functionality.

I've also made it so when you return to the homescreen you'll return to the submenu you were last in.

I've added the following to the Home.xml to make sure the user doesn't have to reconfigure the skin settings:
```xml
<onload condition="Skin.HasSetting(backspacehome.enable) + !Skin.HasSetting(backspacehome.upgraded)">Skin.SetString(backspacehome, return)</onload>
<onload condition="!Skin.HasSetting(backspacehome.upgraded)">Skin.SetBool(backspacehome.upgraded)</onload>
```

This should probably be removed after everyone upgraded.

Please tell me what you think about this and if would merge this into your branch so I can get to work on the home menu settings. There are a couple of bugs (Movie Sets are listed twice for example) and a lot of missing entries (Directors, Tags, etc.)