[kcms/lookandfeel] Support latte layout

• This patch enables LookNFeel KCM to load and unload latte layouts on demand when a looknfeel package is applied from the user. Designers can include in their package a layouts/looknfeel.layout.latte textfile if they want a specific layout from Latte. In such case Latte is also enabling its autostart.
• In case the looknfeel package does not contain the previous mentioned latte layout file then we can safely assume that the user does not want Latte at all and in such case Latte quits and is removed from autostart.
• In order to apply or not the latte layout the user must have chosen to update the desktop layout from the relevant ui checkbox.
• This patch to work needs at least Latte Dock >= 0.10.5
• If the Latte requirement is not met then the user will not observe any changes.