Add action to show a swing tree for selection.

This new action fires up the scalac tree browser on the
selected source in the current editor. This helps track
down position-related bugs, such as issues in hyperlinking,
hovers, completions, etc.

* also fixed 'race condition' errors in the spy view.
Correctly resolve overloaded Java methods in hyperlinking

The Scala selection engine didn't build the correct signature
for Java methods taking array parameters. It turns out that
the special-handling `mapParamType` wasn't needed, and the
existing `mapType` method in `ScalaJavaMapper` was already
working correctly.

Fixed #1000421
Updated `sbt.version` for Scala 2.10 and 2.11 profiles

The version of Sbt 0.13 (master) changed back from Beta1 to
SNAPSHOT, hence we need to update the profiles for Scala 2.10
and 2.11 to pass the right value fot `sbt.version`.

This commit basically reverts the changes in the POM made by
SHA: c4f66e5324a014d7587b4bdfaa9a47f7b3a221b5
Merge pull request #440 from dotta/transient/sbt-master-version-back-to-SNAPSHOT

Updated `sbt.version` for Scala 2.10 and 2.11 profiles
Merge pull request #429 from dragos/issue/hyperlink-overloaded-java-1000421

Correctly resolve overloaded Java methods in hyperlinking
Initialize List and Nil so the XML parser does not introduce race conditions

Fixed #1001708. No test since no reproducible test case.
Correctly handle boundary conditions in the ScalaWordFinder

I reorganized and simplified the logic in the ScalaWordFinder,
and added a few tests. It seems to fix at least the exception
and a couple of other boundary conditions (revealed by pressing
F3 at the very beginning or very end of an identifier, or even
an identifier between `{}`).

Fixed #1001526
Merge pull request #442 from dragos/issue/race-condition-xml-1001708

Initialize List and Nil so the XML parser does not introduce race condit...
Merge pull request #435 from dragos/issue/SIOOB-hyperlink-1001526

Correctly handle boundary conditions in the ScalaWordFinder
Merge pull request #428 from dragos/spy-improvements

Add action to show a swing tree for selection.