Getting demo to run, why is it so difficult. Readme needs an update.

Steps:
1. Download gradle version required `2.1`, using manual method as `Android Studio` is bad in that respect.
2. Change `runProguard false` to `minifyEnabled false` in `sampleapp/build.gradle` and `multilevelexpindlistview/build.gradle`
3. Library projects cannot set the `ApplicationId`, so have to remove that line from `multilevelexpindlistview/build.gradle`
