add option to have spaces in import braces, sort all grouped names together

- added new checkbox to scala code style Spaces tab, allowing to format imports like

 `import java.util.{ EnumSet, HashSet }`. 

Scala ide and some auto formatters can do it, so it can be quite important to maintain same style with idea.
- order of import names in one line is changed from

`java.util.{EnumSet, ArrayList => JArrayList, List => JList, BitSet => _}`

to
`java.util.{ArrayList => JArrayList, BitSet => _, EnumSet, List => JList}`

by sorting all tokens together instead of sorting singles, renames and hidden separately
- Some basic unit tests added
i've also converted ImportInfo to a case class, but maybe it was a regular class for reason.