Improving page load experience for book readers

**Context**
Page loading spinner can affects the overall book reading experience
> Is your feature request related to a problem? What is the motivation for implementing this feature?

**Proposal & Constraints**

> What is the proposed solution/implementation? Is there a precedent for this approach succeeding elsewhere?

I am not aware of the internal reason for page rendering being slow, but one thing that can certainly be fixed here is the loader icon which feels like as if it takes forever to load.
> Which suggestions or requirements should be considered for how this feature needs to appear or be implemented?

Instead of using a loading spinner, css based skeleton loaders can be added. Although the page load times will be same, but its impact on the end user experience will be different ()

**Additional Resources**
https://www.youtube.com/watch?v=0-3GBgRg9ow
https://uxdesign.cc/stop-using-a-loading-spinner-theres-something-better-d186194f771e
https://uxdesign.cc/what-you-should-know-about-skeleton-screens-a820c45a571a

> Add any other screenshots or assets related to the feature request.


**Success Metrics**

> How will you know if this change is successful? What specific metrics are relevant and how do you expect them to change?

**Stakeholders**

> @-tag stakeholders of this feature
@shaneriley

The issue does not name files, tests, or an entry point. Start by locating the current page-loading spinner in the BookReader frontend and review the attached example and linked resources; done means the spinner is replaced with a CSS skeleton loader without changing page-loading behavior.

Written by the indexing model from the issue text.