add 3 tab to main activity
Merge branch 'master' of https://github.com/hieutn/voer

Conflicts:
	Voer/res/values/strings.xml
	Voer/src/vn/edu/voer/activity/MainActivity.java
	Voer/src/vn/edu/voer/service/ServiceController.java
	Voer/src/vn/edu/voer/utility/Constant.java