ball and stick representation should show bond order

[arouinfar]

Noticed during #150. The the ball and stick representation is not showing double or triple bonds. This is a deviation from Java, and is pedagogically problematic.

Example of a molecule containing a double bond

Example of molecule containing a triple bond. (Admittedly, this looks pretty gross in Java.)

[Denz1994]

Great catch @arouinfar. The bonds were being created according to their bond order. However, they needed to be adjusted so the higher-order bonds would be displaced from a specific offset. What do you think about this dev version?

Here are some visuals: Single Bond

Double Bond

Triple Bond

[arouinfar]

Looks great @Denz1994!