add git-bug to the build and test core features in the browser

[happybeing]

Add git-bug to the build, and test display and creation of issues and comments. This depends on the following git-bug issues being completed first:

• make git-bug usable as a package (make git-bug usable as a package happybeing/git-bug#1)
• modify git-bug to use go-billy filesystem and not touch OS filesystem directly (modify git-bug to use go-billy filesystem and not touch OS filesystem directly happybeing/git-bug#2)

[happybeing]

With commit happybeing@9c6f2ef git-bug is integrated and working with this application, which means the work of this issue is complete, in fact very little was needed for this to my surprise because Go can just use things from an app as if they are a package. I had thought I'd need to modify git-bug to achieve this but work was only needed to enable it to compile to wasm, and on getting it to use the go-billy filesystem.

However, I am keeping this issue open because it relies on an issue (happybeing/git-bug#2) which while working, still has outstanding changes to be completed. Once that is closed this issue can also be closed.