[1/2] SystemUI: Network speed indicator

Change-Id: I88e7cdfe20342c695a33383db36bf80bb4ffe009
[1/2] SystemUI: Update network traffic indicator

Android measures the amount of data transferred in bytes,
however, by convention, data rates should be measured in bits
per second.

*Convert the change in total data and time to bits and seconds,
and then divide the amount transferred by the number of
seconds that have elapsed.

*Update the labels and have them use the correct SI prefixes.

*Factor out or add @hide to public methods and constructors

*Remove all Runnables and Messages from Handler queue when
disabled

*Minor formatting changes to stay consistent with Android's
code-style guidelines.
https://source.android.com/source/code-style.html

PS2: Set maximum digits to prevent it from filling the statusbar
PS3: Rebase
PS4: Add ability to display either bits or bytes

Change-Id: I9add610a8d14f5a48f2af0a82ced0c186224e282
[1/2] Base: Upgrade network traffic meter

*Updated class name to be less ambiguous
*Replaced the multi-check in settings with a proper listview
*Added the ability to view up-stream, down-stream or both
*Added the option to change how often it refreshes
*Added a check before it updates the status bar to prevent it from
refreshing everything needlessly
*Added icons to show data direction
*Remove unused style attributes

Icon artwork is courtesy android design downloads
Some features were inspired by previous work done by 0xD34D

OmniGears: https://gerrit.omnirom.org/#/c/5130/

Change-Id: I9f86292a6adbc5e30967df76fae510be248fc38b