add intellij projects to .gitignore
cleanup: Various small syntactic and formatting cleanpus.

Fixes mostly guided by IDE warnings:
- Occasional formatting fix (tab -> 2 spaces)
- toString() -> toString
- def mutableMehtod -> def mutableMethod()
- getOrElse(null) -> orNull
- name boolean parameters on call site
Merge pull request #2 from matobet/minor-cleanup

Minor cleanup