Add a status bar

[AlstonLin]

Right now, all other 3rd party lock screen apps are doing a custom status bar to replace the default one when the screen is locked, and increasing the overlay draw priority to the highest to cover the existing one.

This is a workaround from the fact that other apps can change the status bar color, and make it something other than transparent, which would make the UI of the lockscreen really wierd.

Things that the status bar should include

• [x] Battery percentage (text)
• [x] Wifi (Based on strength)
• [x] Signal (Based on strength)
• [x] Airplane Mode

Obtain icons from here: https://github.com/google/material-design-icons/tree/master/device/drawable-hdpi

[AlstonLin]

It looks like Android N updates actually fixes this problem, so this needs to be tested on older phones

[AlstonLin]

Bug can be seen when testing using Nexus 5 on API 19