- added "databinding" between hovered-on items in the bom of the assembly-step
and the hovered on 3d shape:
 * added all needed boilerplate code
 * added injection of meta data into loaded meshes

- added more notes in main demo.html and NOTES-assemblyInstructions2
- various tweaks and improvements
- internal cleanup/restructuring around bom:
 * hierarchy now only contains partNumbers, not uris of 3d meshes for the different parts
 * a bom containing the uris, title, descriptions etc now needs to be passed to the viewer
 * restructured code accordingly
 * added pre-loading of all meshes for a given step
 * added re-use of geometry (actual 3d data) between instances (for example multiple nuts etc)
 * added progressbar (basic) to show progress of loading assets

- loaded 3d data/bom does not get deleted anymore when changing steps
- improved databinding between assembly-viewer and assembly-step
- styling improvements
- styling & markup cleanup:
 * viewer and current assembly step are hidden before loading of a step is complete
 * restructured markup a bit

- started work on possible system for parsing step by step instructions
 * created a somewhat acceptable peg.js grammar