[2/2] OmniGears: Updgrade network traffic meter

*Implements list preferences where applicable to simplify the settings
*Add the ability to track Upstream, Downstream, or both
*Add the option to change the frequency with which it updates

PS3: add a config to disable network traffic meter
PS6: Update strings and check if stats are supported automatically

Base: https://gerrit.omnirom.org/#/c/5129/

Change-Id: I778d981fb7a57d07127608f99d45936a55ae4898

Conflicts:

	res/values/custom_arrays.xml
	res/xml/bars_settings.xml
	src/org/omnirom/omnigears/interfacesettings/BarsSettings.java