Modernize navigation

Charlie and Kristin created a great design palette for Field Day: fun fonts, bright colors, intuitive icons.

I wanted to keep that but update the navigation to reflect the current understanding of our usage model. To that end, this merge centralizes everything onto one screen, miniaturizes our less-used buttons, and puts database and sensors at the forefront.

No specific activities or fragments other than the main screen (and the deletion of the obsolesced sensor screen) have been changed.

I can foresee a future where we do more data analysis and aggregation through the lab notebook, so I've preserved the notebook icon for future use.

I'm squashing the commit history because most of the individual changes are trivial.