"Loading" and "No data" messages

[garrettjstevens]

In the graphical display and the tabular display, it would be good to have a "Loading" message while the data is being loaded so the user knows that something is happening.

When the loading is finished, if there is no data to show in the displayed area, the tabular display should also show a "No data in this region" or some sort of other message.

May need to add a loading status flag to the client data store.

[garrettjstevens]

Possible implementation for loading message:

• Add "loadingRegions" as a Region[] to volatile section of packages/jbrowse-plugin-apollo/src/session/ClientDataStore.ts
• In loadFeatures in that same file, add currently loading region to "loadingRegions" at the beginning of the action and remove it at the end
• In packages/jbrowse-plugin-apollo/src/LinearApolloDisplay/components/LinearApolloDisplay.tsx, check the currently loading regions (via session.apolloDataStore.loadingRegions) and the displayed regions (via model.displayedRegions), and if any of them overlap, add a "Loading..." message to the component
  • The loading message can be in the corner of the track and overlap the regular track area, since it may still be loading new data when there is already data on the screen

I'll have to think more about the "No data" message

[garrettjstevens]

A loading indicator was added in #523, and a "No data" message is probably not necessary based on observed user interactions.