Update pref store reference in `ScalaSourceViewerConfiguration`
Update pref store references in scanner classes

There was no need to use multiple pref stores, only one is used now.
Replace references to Java partitions with references to Scala partitions

This shouldn't introduce any functional changes beside from the point
that everything related to partitioning (syntax highlighting, auto
edits) have a chance to not work anymore.

Some new Scala partitions are added, they replace partitions located in
`IJavaPartitions` and `IDocument`.

Because this is a no compile-time-save change, it could be that some
references are forgotten, but hopefully my grep-foo caught them all.
Enable Scala partitioning on all Scala files

After all referenes to Java partitions were removed, syntax highlighting
didn't work anymore because the `IDocumentSetupParticipant`, that
intrnally uses Java partitions was inherited from the Java plugin - a
problem which is solved by this commit.
Add new Scala partition to constructor call of `JavaHeuristicScanner`

The previously called constructor forwards to another constructor by
passing Java partition references, which obviously are not the right ones.
Merge pull request #742 from sschaef/remove-java-partitions

Remove java partitions