Improve rendering performance for feature trees

[ekuiter]

When rendering large feature models, the tree layouts render hundreds of SVG elements, causing performance issues. There are some approaches to improve this:

• render less SVG elements per feature model element (likely impairing animations and code quality)
• render large feature models (e.g., > 1000 SVG elements) to a canvas (no more animations, complicates click capturing, rendering the SVG to a canvas also takes some time!)
• profile the drawing process and do some micro-optimizations
• improve the "fit to screen" command so that it is not necessary to draw large feature models, e.g.
  • do not collapse features until the model fits, but expand them until it does not fit (for large models, this should be much faster)
  • warn if the "expand all" operation will be slow
  • when rendering takes long, warn the user and advise him to fit to screen/change to another layout