Change JS `for` counting down trigger from for to ford

As suggested by @SirVer[1], this commit changes the trigger of the
JavaScript `for` snippet that counts down from "for" to "ford". Since
"for" is used pretty often, this will prevent people from needing to
select which one they want from the menu each time.

[1]: https://github.com/SirVer/ultisnips/pull/123/files#r8686514
Add "b" options to JS `for` and `ford` snippets

`for` loops usually appear at the beginning of the line. This commit
makes these snippets more context-aware by adding the "b" option that
prevents them from being triggered if they are preceded with something
other than whitespace, as suggested by @SirVer[1].

[1]: https://github.com/SirVer/ultisnips/pull/123/files#r8686514
Simplify JS `for` snippet bodies

As suggested by @SirVer[1], having `Things[i]` be pre-populated in the
body of the `for` loop snippets is not very useful given the merits of
autocompletion. This commit simplifies these bodies by simply using
`${VISUAL}$0`.

[1]: https://github.com/SirVer/ultisnips/pull/123/files#r8686533
Re-order JS `for` snippets

Now that we have separated the two `for` loop snippet triggers by
changing the one that counts down from "for" to "ford", it feels more
and more like "ford" is a variant of "for" so I am moving it after it in
the file. Also, alphabetical.