Add NoWhitespaceBeforeColonChecker and WhitespaceAfterColonChecker

These checkers assist to be no whitespace before colon, and only one whitespace after colon for [Scala Style Guide](http://docs.scala-lang.org/style/types.html).
The checker covers following statements

#### Value and Variable

    // OK
    val i: Int = 1
    // NG
    val j :Int = 1


#### Function

    // OK
    def foo(x: Int, y: Int): Unit { }
    def bar: Unit { }
    // NG
    def foo(x :Int, y :Int) :Unit { }
    def bar: Unit { }    

#### Class

    // OK
    class Foobar(a: Int, b: Int) { }
    // NG
    class Foobar(a :Int, b :Int) { }

#### Case

    // OK
    val l = List(Dog, Dog, Cat, Dog, Cat).map{
      case i: Dog => 2
      case s: Cat => 1
      case _ => 0
    }
    // NG
    val l = List(Dog, Dog, Cat, Dog, Cat).map{
      case i :Dog => 2
      case s :Cat => 1
      case _ => 0
    }

This style is adopted by most of the Scala standard library.