Basic links added

We now have basic links between the elements. The positioning of elements makes the links look a bit off, but they're here and they're uh...straight lines
Added a test RNA strand

Added an RNA strand to the demo, fixed a bug with Uracil rendering
Separated view from model

We now have strand visualisations which operate separately from strands. Each strand at the moment has a separate view, this allows us to have multiple strands on one svg while keeping the data of each strand separate.