Units should stay the same when changing stations

[Adelle-Pitsas]

• Unit system selection reverts back to English from Metric when you change stations or change time range. Works okay with Datum selection change (hard to show in a screen shot but easy to replicate!)

Originally posted by @youngmorse in #2701 (comment)

[abkfenris]

We might want to think about using URL params and/or cookies for current unit and datum selections and to persist defaults for users.

[Adelle-Pitsas]

Updating here as I've been working on the unit selections and default state on WL pages. PR #2899 puts unit selection in session storage to persist over url changes and refreshes. It will revert to default if a user opens a new tab (a new session).

Datum selection is currently included in url params and persists on sensor/url change and refreshes. It defaults to MLLW when a user first selects a sensor from the base /water-level url