Add a default board

[benjaminpjones]

Based on discussion on #137, this is a proposal to replace Board .vue files with a simple JS function. It's a larger PR, so to summarize:

• Introduce DefaultBoard (a selector for MulticolorGridBoard and MulticolorGraphBoard)
• Introduce uiTransform (a function that can update the config and state to fit the DefaultBoard interface)
• To validate, migrate FreezeGo to the DefaultBoard and test.

Testing: Freeze go and other variants seem to show up fine in the game list, game view, and demo view.

For example, here is the demo view:

[benjaminpjones]

Changes after accept:

• Rebase (fixing minor merge conflict with #321 in GameListItem)
• Use standard import