feat: project-centric extension internal model

This MR finishes #558 (closed), it removes WrappedRepository in favour of the new ProjectInRepository. The extension has been almost completely migrated to the new model in previous MR's but this MR replaces the extension core.

User facing changes

• There is no gitlab.instanceUrl setting anymore. Either we'll match the git "remote URL host" with "token GitLab instance URL host" (99% cases) or the user has to create the link manually (visible in the multiple-projects-after screencast).
• The preferred remote is no longer stored in settings.json. Instead, we store it in local storage. This is fixing a bug #546 (closed)
• Context menu on repositories where automatic project detection couldn't find unambiguous GitLab project
  • Select GitLab project context action if we detected multiple projects. In the screencast, this happens because the extension has two remotes: git@gitlab.com:gitlab-org/gitlab-vscode-extension and git@gitlab.com:gitlab-org/security/gitlab-vscode-extension - before, user had to click on the repository item and select a remote, but they didn't know if the remote contains a GitLab project, now we only offer detected projects
  • Manually assign GitLab project context action on repositories where we didn't detect any GitLab projects. This can happen in edge cases where users use local folders as remote URLs (#418 (closed)) or when they use SSH aliases defined in ~/.ssh/config (#537 (closed)) this issue couldn't be previously resolved by the user
  • Clear selected project - this removes the previous selection
• The project parent item is visible even if there's only one project (you can see in single-project-before we hide the project parent item once the user selects the remote) - I chose to do this so the user can use the Clear selected project context menu. In future iterations, we can come up with a different UX treatment.

	before	after
single project	single-project-before	single-project-after
multiple projects	multiple-projects-before	multiple-projects-after

Related to #558 (closed)