Bug 1039931 - [gaia][system] Replace __proto__ with Object.create

* Remove usages of __proto__ in the system app.
Bug 1038326 - Fix layout issues with searchWindow and children. r=alive
Merge pull request #21853 from begeeben/1039931_replace__proto__

Bug 1039931 - [gaia][system] Replace __proto__ with Object.create, r=alive
Bug 1039984 - [System] Trying to open a smartcollection after killing the Homescreen do nothing.

Allow Homescreen application window to be killed as other windows.