Handle origins with multipe visit types in browse interface

SWH data model was designed such that origins can have multiple visit types.

Until recently, we never had such cases in the archive but it is no longer true since the deployment of the new nixguix lister. In particular we now have origins that can have visit types git and git-checkout

Currently, the webapp does not filter on the visit type when fetching the snapshot associated to the latest visit. So when browsing a git origin whose latest visit type is git-checkout only a single directory is displayed without any revisions info as git-checkout visits only archive a directory targeted by a tag or a commit, which is quite confusing.

In order to fix that issue, we need to display the visit type in the browse Web UI but also implement visit type filtering using a new query parameter in the URLs but also in the Web UI by adding a drop down in relevant views.