refactor log commands

Prompt the user for the range in the `interactive' forms of
`magit-log-ranged' or `magit-log-long-ranged'.

Previously this was not only done outside of the `interactive' form
of these functions but inside of `magit-log'/`magit-log-long' which
are called by the former.

This is wrong for two reasons:

(1) Whenever possible minibuffer input should be read in the
    interactive form.

(2) `magit-log'/`magit-long-log' only ever used the range when
    called by `magit-log-ranged'/`magit-log-long-ranged'.

`magit-log'/`magit-log-long' now take a RANGE as first argument,
replacing the "ask the user for a range and use that" switch
previously used.

Since this change affects almost all lines seize the opportunity
and move the "Logging" section into the toplevel "Acting" section.
name the reflog commands correctly

Rename `magit-reflog' to 'magit-reflog-head' and
rename `magit-reflog-ranged' to `magit-reflog'
reverting 8fcae59c9f15c3519fc9145b7b331ee8c2df80bf.

Also read the rev in the interactive form of `magit-reflog'.
For rational see 13d21ce5ac431ca906e2d1862d6e01e488bfd8da.