Improve "import in progress" screen
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Work on this issue](https://contributors.gitlab.com/manage-issue?action=work&projectId=278964&issueIid=27554) - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=27554) </details> <!--IssueSummary end--> Right now, if you import a project and it takes more than a few seconds, the page will continue auto-refreshing itself. This looks sloppy as the page will "stutter" every few seconds as the page re-renders. We should use javascript polling on the frontend to make this more seamless. We also ought to replace the old loading spinner with the new design from `gitlab-ui`. ![import-in-progress](/uploads/ec0d73878ba537afe22d032fdd0c4f66/import-in-progress.png) We could also take a page from github's design and place a friendly SVG illustration on this page as they do when forking/importing a repository. ![github-fork-illustration](/uploads/48ff9e70bfd8844cce20d77dbda5208d/github-fork-illustration.png)
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