ObsPy's waveserver.py (and associated methods) do not handle an empty
buffer returned from Edge's earthworm server. In short, they generate
a None value instead of an empty byte string as one might expect (and
they clearly did expect, since they attempted `len(dat)` where dat
was expected to be a byte string, but was a None object if/when Edge
had no data. This fix employs a try/except clause to generate an
empty string if the waveserver client fails with a TypeError, as is
the case when Edge returns an empty buffer.

Erin (Josh) Rigler authored 6 years ago and Claycomb, Abram Earl committed 6 years ago

- allow adjusted and provisional strings in --type controller argument
- allow adjusted, provisional, and definitive strings in _get_url() in TimeseriesFactory
- return appropriate abbreviation for adjusted/provisional data type
- translate adjuste/prvisional to A0 location code in EdgeFactory
- only write out DECBAS for variation/reported data types
- translate adjusted/provisional to A0 location code in IMFJSONWriter.py
- in several places I set it up so that 'variation' and 'reported' were synonymous,
  although I am not sure I found every such instance.

Fixed npts issues in create missing and channels as well as a unit test. Also cleaned up the unit test code for syntax and linting.

Also update the maximum channel length to 4 in IAGA2002Writer to
allow for the use of 'DIST' as a channel.