Integration of all four datasets

[keatonwilson]

Currently, map data is limited to just tidal amplitude. The other three datasets need to be implemented. This will involve:

1. Getting velocity data preprocessed and loaded in the app (@keatonwilson will handle)
2. Generating appropriate plotting schemes for data
3. Hooking up to reactive input components

[keatonwilson]

Data have been pre-processed, but next steps are to hook Tidal Current, Stratification and BSS into reactivity. Probably in this order, as BSS is going to take some work. @jessicaguo will take current and stratification to start. @keatonwilson will take a look at bed stress.

[keatonwilson]

@keatonwilson Will check with Sophie on gradient tick box - do we just want categories (would be nice).

[jessicaguo]

Done!