Refactor ImplicitVarPorts usage

[PhilippPlank]

Objective of issue: ImplicitVarPort objects are added to ProcModel classes as attributes when RefPorts are connected through connect_var(). This needs to be changed to PyVarPort objects instead.

Lava version:

• [ ] 0.4.0 (feature release)
• [ ] 0.3.1 (bug fixes)
• [x] 0.3.0 (current version)
• [ ] 0.2.0
• [ ] 0.1.2

I'm submitting a ...

• [ ] bug report
• [ ] feature request
• [ ] documentation request

Current behavior:

• ImplicitVarPort objects are added to ProcModel classes as attributes when RefPorts are connected through connect_var().

Expected behavior:

• Corresponding PyVarPort objects should be added to ProcModel classes as attributes when RefPorts are connected through connect_var().

[tim-shea]

@PhilippPlank Is this still an issue?