Documentation for class properties should be placed with the declaration, not the instantiation.

[pixelzoom]

For #84

This is violated in every .ts file that I've inspected.

From https://github.com/phetsims/phet-info/blob/master/doc/typescript-conventions.md#documentation-for-class-properties:

Documentation for class properties should be placed with the declaration, not the instantiation. For example:

class Person {

  // First and last name, separated by a whitespace
  readonly name: string;

  constructor( name: string ) {
    this.name = name;
  }
}

[marlitas]

Moved what appeared to me to be declarative documentation outside of the constructor. Ready for review from @chrisklus.

[chrisklus]

Thanks @marlitas! review complete. any additional updates were committed above. Closing!