TrafficMeter: added option for Display mode
"Download manager only" option has been replaced with extended "Display
mode" option list which allows to show traffic meter:
- Always (when connection available)
- When progress bar in status bar is showing
The last option is new and allows to show traffic meter automatically
when there's progress bar in status bar showing for some ongoing
transfer (bluetooth transfers ignored)
Conflicts:
	res/values-es/strings.xml
	res/values-fr/strings.xml
	res/values-hu/strings.xml
	res/values-ja/strings.xml
	res/values-nl/strings.xml
	res/values-ru/strings.xml
	res/values-tr/strings.xml
	res/values-zh-rHK/strings.xml
	res/values-zh-rTW/strings.xml
	res/values/arrays.xml
	res/values/strings.xml
	src/com/ceco/gm2/gravitybox/GravityBoxSettings.java
	src/com/ceco/gm2/gravitybox/TrafficMeterAbstract.java