`Workouts`: create NewWorkout component and API endpoint

[Seerden]

See #4

Changes:

• [x] implements a NewWorkout component (client-side route: /workout/new that builds a new workout with exercises
• [x] implements a backend route POST /exercise/workout that handles insertion of the newWorkout object passed from the client into the database as a combination of workout and exercise rows

Miscallaneous

• [x] downgrade jest to non-alpha version
• [x] extract bits of config for fetch functions to a constants helper file
• [x] copy-paste types from server to client so that we don't have to redefine them client-side
  • [ ] there has to be a better way to handle this that's not "just switch to GraphQL with codegen"
• [x] add a client-global Maybe type
• [x] tweak Title component styles
• [x] implement Subtitle styled component

[Seerden]

Current status:

Remaining tasks:

Client:

Functionality:

• [x] implement state
• [x] make unit selector (kg/lbs) functional. Probably want to unify this as a single user-defined setting. Then convert visually instead of forcing the user to specify everywhere.
• [x] implement event handlers to update state
• [x] implement POST helper, hook, event handlers

  UI

• [x] collapse all except one NewExercise
  • [x] requires creation of CollapsedNewExercise component

[Seerden]

Current state:

To-do:

Functionality not done yet. Have some new to-dos for the styling though:

• [ ] highlight valid NewExercise fields
• [ ] add styling to 'Unnamed exercise' to distinguish it from named exercises
  • [ ] better yet: add conditional styling on CollapsedExercise components if the exercise isn't valid in general, even if it does have a name
• [ ] decrease ActionBar button widths on small viewports (it's overflowing now)

[Seerden]

Also implementing server-side functionality in this PR:

Server-side to-do:

• [x] set up /exercise router
• [x] implement database model for exercises and workouts
• [x] write insert query for new workouts
  • [x] expose the query at a POST route

Client-side to-do:

• [ ] implement newWorkout validation and feedback messages
• [x] implement fetch function and mutation hook
• [x] think of onSuccess handling - do we want to redirect somewhere? There's no other pages yet so this'll have to be done later Q: also, does a mutate({onSuccess: ...}) overwrite the useMutation(..., {onSuccess})? Ideally we'd want a built-in onSuccess that updated the workout's value in queryCache, and an additional onSuccess at the call-site that handles the navigate() call. A: does not overwrite. Both onSuccess callbacks get called. The one from mutate() gets called last.
• [x] filter out invalid new exercises on form submission.
  • [ ] when there are invalid exercises present, add an intermediate step 'Are you sure you want to submit? Not all exercises are valid: invalid exercises will not be saved'

[Seerden]

Merging this for now because the happy path is functional. Keeping the related issue open since there's still work to be done here.

Open tasks:

• [ ] test components
• [ ] test helpers
• [ ] handle onSuccess once authentication and workouts overview page are implemented