Updated maven surefire plugin version.

Update path to stratosphere-dist folder in README.md

Fixed translation bug where solution set was first input to the join.

Fixed concurrent modification in memory release.

Removed Nephele plugins

Fixed erroneous execution graph test.

Updated maven surefire plugin version.

Fix bug with user-code wrappers

The problem was that the user code wrapper was not deserialized from the
config using the user-code class loader. Now we jave a custom
ObjectInputStream that uses the user-code class loader to resolve
classes.