Add a spinner wheel when beadplot is rendering

[GopiGugan]

For larger beadplots, it takes a longer time to render when initially loading the page. We should add a spinner to let the user know that the page is still loading

[ArtPoon]

We already have a spinner at the top of the page (below the search bar) that activates when loading a new beadplot - does this need to be moved somewhere more prominent?

[ArtPoon]

I suppose we could try the following:

• move the current spinner to be centered above the beadplot area instead of placed on the left
• grey out or fade out bead plot area and display spinner in the middle

[ArtPoon]

@GopiGugan modified the initial dialog so that the user cannot dismiss it until the first beadplot loads