GPII-900: Adding more functionalities to Gruntfile.js

Global tasks:
* Added uninstall
* Renamed installPrivilegedApk as installPrivileged
* Added uninstallPivileged
* Added clean
* Added distClean
* Added required code for start task

Shell tasks:
* Added cleanApk
* Added removeBuildFolder
* Added uninstallJs
* Improved installApk
* Added uninstallApk
* Added uninstallPrivilegedApk
* added distClean
* added startGpii

Also:
* Fixed a few issues
* Linted Gruntfile.js