added standalone multisort implementation to file_browser example

[telamonian]

Adds a standalone implementation of multisort to the file_browser.html example. Slightly simplified, but mostly equivalent to the one recently removed from events.js:

[telamonian]

Multicolumn sort now tree-aware:

Got a bit messy, but is fully functional. I'll try and clean it up

Cleanup done. Tree-aware multisort implementation still significantly more complex than multisort implementation for flat lists. The sort-in-place pattern becomes impractical, and you need a touch of recursion to deal gracefully with the arbitrary depth tree.

Which made me consider: does V8 do tail call optimization?

[telamonian]

This test is valid, but runs into some kind of issue with scrollTo when offset === 12. Basically, the failure seems to occur due to the fact that scrollTo(0, 24, 4, 300) scrolls to the same row as scrollTo(0, 25, 4, 300):

  ● file_browser.html › sorts tree filebrowser › uses same sort at all levels, sort then expand tree

    expect(received).toEqual(expected) // deep equality

    - Expected  - 1
    + Received  + 1

    @@ -3,10 +3,10 @@
        "add charlie/",
        "add baker/",
        "add able/",
        "file_89.txt",
        "file_88.txt",
    -   "file_87.txt",
    +   "file_86.txt",
        "file_86.txt",
        "file_85.txt",
        "file_84.txt",
      ]

[telamonian]

I added sorting tests to file_browser.test.js. The tests for sorting a flat filebrowser all pass. The tests for sorting a filebrowser tree with several expanded nodes work in principle, but are currently failing due to an issue with scrollTo (see note in code here).

@texodus Not sure exactly what the problem is, but the scrollTo issue/test failures are sensitive to the exact value of viewport height. Any thoughts?