Resolves #174 with the following changes:

  1 - Side-mounted engines now can 'see' fuel through their surface mounts.
  2 - Now detects when an attachment can't carry fuel (attachment is strut)
  3 - Now traverses yellow fuel lines to find fuel.
Could there be a single function that returns boolean given two Parts?  True if fuel can flow from part A to part B, false if it can't?