[DRAFT] .ipynb model

[cameron-toy]

TL;DR: Dashboards will now exist embedded in notebook metadata and be openable directly from the file menu. This means they're fully self-contained, have their own kernel, and don't require a notebook from the same .ipynb file to be open. .dashboard files still exist for now but that may change.

What's new

User-facing changes

• Dashboards with their own kernel can be saved to and opened from .ipynb files. Embedded dashboard functionality is currently very limited (can basically just add and move widgets).
• Multiple dashboards can be embedded in one notebook. If multiple embedded dashboards are present, the user will be prompted to pick one when opening the notebook as a dashboard.

Code changes

• New dashboard widget, output widget, dashboard layout, dashboard model--almost everything has been re-written to support embedded dashboards.
• Undo/redo now handled by a much lighter UndoManager instead of the modified CRDT datastore.

Todo

End goal is that embedded dashboards have all the functionality dashboards from .dashboard files do. This includes:

• Adding, removing, moving, and resizing outputs.
• Grid-based and absolute positioning of outputs.
• Edit and preview/present modes.
• The ability to change the grid and dashboard size.
• Toolbar.
• Overlap resolution.
• Undo/redo.