Test refactor
Fix for getting nonexistent keys
Consistency, TOOWTDI

- Removed GetBool, SetBool (in favor of GetKey<T>, SetKey<T>)
- Renamed GetString, SetString to GetKey, SetKey (consistency)
- Renamed GetArray, SetArray to GetKeyArray, SetKeyArray (consistency)
- Removed SectionNames property (still available through Sections.Name)
- Removed operator [] (avoids confusing - should it retrieve key or section?)
  (still available through GetSection)