Visualizations

This pull request contains a refactor of `boardApp` to make the process of adding a visualization cleaner. See [readme](https://github.com/Locu/kronos/blob/visualizations/jia/README.md) for detailed information on the structure of a visualization module.

The existing time series and table visualizations have been converted to the new format and a new gauge visualization was added as a simple test. The gauge is a good reference/hello world visualization because it is so basic.

The only changes to the panel model are in cache, so this it is all backwards compatible.
no seems fine to use this