More robust WorksheetsManager: don't die on unhandled exceptions.

I noticed the worksheet manager actor died on some uncaught exceptions. This
commit makes it log and continue (since it's a singleton instance in a lazy val,
the only workaround is to restart eclipse). Also, noticed that closing a Scala
project causes `unit.scalaProject` to throw, so wrapped that into a `Try`.

I didn't generalize this treatment because in most other cases there is no
good way to recover from missing an open project.

Fixed #129
Use project-specific compiler settings when evaluating a worksheet.

No test since there is no easy way to trigger some observable effect from
compiler settings, other than using compiler plugins (and continuations are
missing from the 2.11 build).

* -deprecation or -feature won't work because warnings are not reported (see #174)
* the continuations plugin isn't part of 2.11, so tests would only work in 2.10

However, I think the integration test isn't really necessary: `scalacArguments`
is part of `sdt.core` and used by the sbt builder.

Fixed #173
Merge pull request #175 from dragos/issue/use-compiler-settings-173

Use project-specific compiler settings when evaluating a worksheet.
Merge pull request #176 from dragos/issue/robust-worksheets-manager

More robust WorksheetsManager: don't die on unhandled exceptions.
Update package names to the new package structure.

Fixup for scala-ide/scala-ide#636
Adds back dependency to sdt.core.test
Merge pull request #180 from skyluc/new-package-structure

Update package names to the new package structure.
Bumps to next dev version 0.2.4-SNAPSHOT
Increase timeout value to stop failing the test that runs first (warmup scala compiler might take longer than 5s on a loaded system).

Also added more info in the failure message.
(cherry picked from commit 4f7988de65c07b8909d56fd9f826623fa492b74d)
Merge pull request #181 from skyluc/issue/bump-version

Bumps to next dev version 0.2.4-SNAPSHOT