Updated instructions for IntelliJ IDEA + updated dependencies

The instructions for IntelliJ IDEA have been updated to use import SBT project instead of gen-idea. Importing an SBT project keeps IDEA in sync. Also testing frameworks such as ScalaTest are difficult to integrate into IDEA without using the import method. With these instructions the IDEA run configuration for Android works as normal.

Additionally, proguard is upgraded to 5.0 to prevent Java version errors.