[BB-3778] Implementing Static page for Dashboard

Created by: spokerman12

We're fulfilling the following user story:

"As on OpenCraft Developer I want to implement static preview for dashboard page, so that user can get a real-time feel of how the customization will look like"

JIRA tickets: BB-3778, Gitlab issue

Dependencies: None

Screenshots: See Gitlab issue

Merge deadline: "None"

Testing instructions:

1. Pull this branch to your local OCIM environment
2. Log with a test account; if you don't have one, put a return on top of validate_available_subdomain in registration/models.py, and a dummy string in lmsUrl = props.activeInstance.data.lmsUrl; on frontend/src/ui/components/Header/Header.tsx. That should be enough for you to create an account. Then, make sure that account's appserver is successfully provisioned and there are both an instance reference and a Open edX deployment for your user. You can do this on /admin. Then, go to http://localhost:3000/console/theming/preview-and-colors
3. To test the dropdown, add:

  courseList: {
    defaultMessage: 'Course List',
    description: 'Course List dropdown item'
  }

to PreviewDropdown's displayMessages.ts so there's another option, which will hide the current preview component.

Author notes and concerns:

1. This should be merged before BB-3787 is started or after it's completed (which would require a minor update)
2. We're changing the ThemeAndColorPreviewComponent's name, but not its routing.
3. Currently we have a snapshot test; I'd implement a unit test for clicking the dropdown but that will be better implemented after BB-3583 is merged.

Reviewers

• @0x29a