Create AttributeSet for use by Nodes and Ports #81

Not doing verification against list of possible attribute names and
types yet.
Rename to Attributes, use in more places

Updating Connection and Constraint to use Attributes abstraction.

updating unit tests as well.
Remove unused imports
Other java style warnings.

Other warnings, except for unused local/member variable warnings.

ArrayList without type gives an Xlint:unchecked warning.
Merge pull request #107 from TysonAndre/quickfix

Fix java warnings and lint errors (everything except unused variable warnings)
Merge pull request #101 from TysonAndre/attributeset

Create AttributeSet for use by Nodes and Ports