Log, Files context menu for selected commits: show working tree commands

1) Give back context menu items of non-head commits

It seems SmartGit 20.1 Preview 10 (2020-02-13) from changelog-20.1.x.txt updated:

```
- Log:
  Files: right-clicking a file in a non-head commit only shows now external tools that operate on that commit
```

Now it is really not easy to use `Reveal in explorer` or `Edit` command from files' context menu when we are
browsing commit histories or file log history. I also try to add my own external tool, but not show too.

Hope they can come back.

2) Show `Open in Git-Shell` from context menu of directories in Files.

It is complicated to use `Open in Git-Shell` in SmartGit,  this menu is always grey and unclickable unless
we focus on the **Repositories Window**. Hopefully it can be show at the context menu of directores
in Files.