Bug 1007281 - [Homescreen] bookmarking sites will place icon on its own row with a horizontal Row separating it

https://bugzilla.mozilla.org/show_bug.cgi?id=1007281

The item list in the vertical homescreen always ends with a divider. This patch simply ensures that we don't append a bookmark after the last divider, and adds an integration test for it in which we build a base for bookmarks testing.