[FLINK-1007] Clean up and refactor on Scala and Java code

First cleanup attempt, mostly on Scala code, to follow guidelines from http://docs.scala-lang.org/style:

1. Remove return statement from Scala code where it is not necessary (end of method definition)
2. Remove extra semicolon (;) from Scala and Java code
3. First drop to abide to 100 chars per line for Scala code.
   Will send another PR for other files as I have encountered.
4. Remove parentheses for empty argument methods that do not have side effect
   (see http://www.artima.com/pins1ed/composition-and-inheritance.html#i1343251059-1)
5. Remove unused import statements in Scala code as I have encountered them.

This is first drop to refactor and clean up Scala code to see comment/ response from community.
Additional PRs for follow up code will come as needed.

Comments and suggestions are welcomed.