Add ticks to slider

Description

This adds tick marks to the slider to give the user a sense of how many date options there are.

Changes Made

Add span elements and distribute along slider to serve as ticks.

How to Test

Pull changes locally, run npm run dev. You'll need the dev token in your root directory to build the site.

MR t-shirt size

• extra-small (e.g., update color scheme)
• small (e.g., add tooltip to chart)
• medium (e.g., add new static chart, add new pipeline output)
• large (e.g., initial data processing pipeline, interactive chart)

Timeline for review

• ASAP - blocker for deployment
• Today - blocker for ongoing work
• Next couple of days
• This week
• When reviewer has availability

Review Needs

Does this MR include data processing, modeling, or visualization code that will require domain review prior to release?

• Yes, and I have opened an issue to document the need for review, using the DomainReview issue template
• Yes, and a domain review issue already exists
• No

Related Issues

#20

Additional Notes

NA

Merge Request Checklists

• Code changes adhere to best practices documented in README.md
• Code has been cleaned the way Vue likes it - run npm run lint
• If applicable, the need for future domain review has been documented in an issue
• Below section documents which browsers the site has been tested on:
  • Desktop/laptop
    • Chrome
    • Safari
    • Edge
    • Firefox
  • Mobile device
    • Chrome
    • Safari
    • Edge
    • Firefox