Exclude all network fetcher tests from Travis CI

The fetcher tests are too problematic to run as CI tests.  They do
not provide the utility that they are supposed to, produce false
errors about the correctness of the code and code breakages, and
get in the way of our workflow.

As we have discussed, testing of provider endpoints should be done
by means other than automated tests.  For the time being, the
fetcher tests will still execute in the course of normal "all tests"
runs that we perform ourselves in order to run tests requiring
authentication and network access.
Add Missouri Hub profile (#7617)

- Add MissouriMapper and related tests
- Add lib/textnode.py
- Add `spectype' module with list of valid types.

Notes:
- Subject strings are split on semicolons in
  MissouriMapper.map_subject().  Splitting is done with the `shred'
  pipeline module in some other profiles.
- MissouriMapper overrides the title mapping performed in
  OAIMODSMapper.
  See https://issues.dp.la/issues/7617#note-19, item 4.
  OAIModsMapper was designed to treat various attributes not relevant
  to Missouri and appears designed to take the last title element it
  encounters.
- Titles and descriptions are assigned as lists.
- As with OAIMODSMapper's treatment of spatial data, we filter out
  hierarchicalGeographic properties that are not in the allowed list.
  Unlike OAIMODSMapper, we assign spatial.name with the value in
  spatial.continent if there are no other fields.