Added new port height specific to code blocks

Background: 
Changing the port heights to match line spacing in code block editor affected the port heights for all other nodes in general. We wish to maintain the port heights the same for all other nodes. 

This PR fixes this issue by adding a separate port height value specifically for code block ports.

@Benglin please review.
If caller chooses to use this constructor, then its intention is to have the ```height``` set, there's no point in defaulting it to ```0```. I know you did this to avoid updating thousands of files, so let's restore the original constructor with two parameters. Then put ```Height``` property alongside ```VerticalMargin``` with both getter and setter. ```PortData``` is a lightweight data structure, there's not much we are going to get out of the read-only property anyway.