Add pom.xml for Maven
Add .travis.xml for travis-ci
Update README.md
Add noHistory tag to all activities
update gitignore for Android Studio
Merge branch 'master' of github.com:asilyihong/Escape

Conflicts:
	.gitignore
1. reformat code in Android Studio.
2. add random type at starting game.
1. add a event level in preference
2. add a interface in Disaster
1. add abstract function getLevelCount() in abstract class Disaster
2. implement abstract function in which class inherits from Disaster