Tests table: auto expand/don't group if group has only one item.

[mentonin]

The tests table in /test/<tree_name>/<git_branch>/<commit_hash> groups tests by their path. However, in many cases paths have only one test or subpath associated with them. I suggest ignoring grouping if it groups only one item, to ease navigation.

With this change, a tree that looks like this:

.
├── A
│   └── p
├── B
│   └── C
│       ├── q
│       ├── r
│       └── s
└── D
│   └── E
│       └── t
└── F
    └── G
        ├── H
        │   └── u
        └── I
            └── v

Would instead look like this:

.
├── A.p         # single test in a group
├── B.C         # single group in a group
│   ├── q
│   ├── r
│   └── s
├── D.E.t       # multiple levels compacted
└── F.G
    ├── H.u
    └── I.v