Move Mobile Tools' own implementation of device groups and detection to a submodule

Mobile Tools currently implements its own hooks to provide default device groups and detection. This code should be offloaded to a submodule for a number of reasons:

• Easier readability of mobile_tools.module
• Removes special casing of Mobile Tools' implementation of its own hooks (if detection = "mobile_tools" do something special)
• Reduces the amount of code that has to load on every request
• Gets around the current name collision problem of having the hook and implementation having the same name