Restructuring strings_from_apk

- Changing name of jar to appium_apk_tool
- Added Main and supporting helper classes for parsing name from AndroidManifest.xml
- For https://github.com/appium/appium/issues/2792
- Added new compiled apk tool jar but not using it because it needs java 1.7, so we can use latest apk tool in future. 
- Added instructions in readme.md