Draft: Support multiple APIs

This MR implements Support new gwdatafind server APIs (#28) by refactoring gwdatafind.api into a subpackage, and implementing a decorator for the gwdatafind.ui methods that selects the xxx_path function from the right API module dynamically.

Also adds a new -A/--api option for the command-line interface.

.gitlab/ci/analysis.yml

-# ---------------------------
-# Code Quality workflow
-# ---------------------------
-
-include:
-  # https://computing.docs.ligo.org/gitlab-ci-templates/
-  - project: computing/gitlab-ci-templates
-    file:
-      # https://computing.docs.ligo.org/gitlab-ci-templates/python/
-      - python.yml
-  # https://docs.gitlab.com/ee/user/application_security/dependency_scanning/
-  - template: Security/Dependency-Scanning.gitlab-ci.yml
-
-# -- code quality -----------
-#
-# These jobs check the code for
-# quality issues
-#
-
-flake8:
-  stage: Code quality
-  extends:
-    # https://computing.docs.ligo.org/gitlab-ci-templates/python/#.python:flake8
-    - .python:flake8
-  needs: []
-  variables:
-    # don't fail the pipeline because of linting issues,
-    # these are presented in the code-quality box in the
-    # merge_request UI
-    FLAKE8_OPTIONS: "--exit-zero"
-  before_script:
-    # pick requirements out of the metadata
-    - |
-      REQUIREMENTS=$(${PYTHON} -c "
-      from setuptools import Distribution
-      dist = Distribution()
-      dist.parse_config_files()
-      for req in dist.extras_require['lint']:
-          print(req)
-      ")
-    # install things
-    - !reference [".python:flake8", before_script]
-
-# -- dependency scanning ----
-#
-# This job checks for dependency
-# issues
-#
-
-dependency_scanning:
-  stage: Code quality
-  needs: []
-  before_script:
-    - |
-      python -c "
-      from setuptools import Distribution
-      dist = Distribution()
-      dist.parse_config_files()
-      reqs = dist.setup_requires + dist.install_requires
-      for extra in ('test',):
-          reqs.extend(dist.extras_require[extra])
-      print('\n'.join(reqs))
-      " | sort -u > requirements.txt