Controller cannot process sub-minute starttime/endtime intervals.

Previously, the endtime-starttime interval being processed by the
`run_as_update` method would shrink by 1 (second) with each recursion.
This ultimately broke `run_as_update` when processing anything other
than 1-second data, but it wasn't obvious because we rarely had to
actually recurse. There is a little trickery now to ensure that user-
provided starttime and endtime are inclusive of the full first
(most recent) update interval, while subsequent, calculated, endtimes
are set equal to the prior starttime minus specified output_interval
(e.g., 'second', 'minute', etc.).

It turns out that none of the factories currently being used in
production expects bytes as input, and in fact, Util.read_url()
converts everthing to a string anyway, so a BYTES-oriented input
would couldn't not possibly be working. So, just remove all use
of BYTESIO, and instead use only STRINGIO.

This is a bandaid to allow the `--input-url` option to be used to
read in single files. It adds zero functionality beyond what already
existed when the `--input-file` option was used.

Also, fixed controller's get_output_factory to initialize the
MiniSeedFactory class when --ouput is miniseed

Updated command line argument for output factory

Remove conversion factor arguments, add tests, fix how metadata is accessed and make convert method "public"