[WIP] New mockup with vuex

[obulat]

Description

New design is implemented, including new VerticalStepper component for Stepper.
Data shared among various components is moved to vuex store for easier handling.

Other information

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• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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[akmadian]

It's nice to see lots of defunct components being cleaned up!

Some specific things:

• Now that the vertical stepper is the stepper, I think it would make sense to rename it simply to "Stepper", or "Steps", then renaming the VerticalStep component to simply "Step", or something like this.
• The store still needs to be moved to ./src/store/index.js from ./store/index.js
• It seems to make more sense to me to have the Stepper component manage the steps array that is currently in state, additionally, moving the enabledAndVisibleSteps array to the Stepper component. Is there a reason that they are managed by the state? Are these arrays used only by the stepper and its children, or by other components?
• I'm seeing some choppy behavior when transitioning between selected steps. This may be due to now using VueX bindings for changing selected step instead of having the VerticalStepper component itself manage this. The update to the state would take time to propagate, thus making the transitions choppy.

Overall, looks good! I think it would be good to move more stuff from the store into the VerticalStepper component. A good test would be to ask yourself if the information or method in the store is only used by the stepper, or its children. If it is, it's probably good to move it out of store. In general, I think of the purpose of store as being to track data and global state, not manage behavior - that's for components.

[akmadian]

Looks much better! I like how slim the state is now, I think "the division of labor" makes much more sense.

There are a number of text and styling differences between this branch and the Figma, but I assume these will be taken care of in a subsequent PR. Go ahead and merge whenever :)