Rename fj-host to fj-app

[hannobraun]

The name fj-host makes sense from the perspective of the plugin system (it's an application that hosts model plugins), but I think it doesn't make a lot of sense from a user's perspective. I think fj-viewer is a better name, as that's what it is: A viewer for Fornjot models.

Here's how I'd like to go about this:

• Rename the crate.
• Change nomenclature around the repository; code, README, etc.
• Leave placeholder crate in fj-host directory. Include a README that points to fj-viewer
• Add blocked issue to remove fj-host from repository after next release.

[hannobraun]

I found some notes on how this transition should be done. Updated the issue description accordingly.

[hannobraun]

I think there are good reasons against calling the app fj-viewer, as suggested here:

• At some point in the future, we might want to have an fj-viewer library, so different viewer applications can be build .
• We might include editing features in them at a later date.

Both cases would require another rename. Since this is the end-user-visible face of Fornjot, each rename is unfortunate.

Maybe it would be best to just call is fj-app. That name is future-proof and won't conflict with any libraries we might extract later.

[hannobraun]

I've decided to call it fj-app, as per my previous comment.

[hannobraun]

This has been completed. #358 has been opened to track the removal of the fj-host placeholder crate. Closing.