New feature: Ability to disable the sides of certain nodes from connecting with tubes

[oversword]

This is part of the fix for this issue joe7575/techpack#67

I thought the best way to do this was to add a new feature to tubelib, that would allow you to describe which faces of a node can and cannot be connected to with a tube.

There are several ways this could be done:

• Use a list of allowed directions
• Use a list of disallowed directions
• Use a flag like "face only", which can then be used with param2 to disallow other faces from connecting