Generate seed data for dev/staging using factories

[chris48s]

Closes #115

This PR adds a django management command init_data which can be used to populate the DB with some test data and removes the existing JSON fixtures.
The test data generated is random and meaningless, so you'll end up with a resource called "Road stage could least" tagged with "blue" and "head", but as the models and tests evolve the test data we can generate should evolve with it. It also gives us flexibility about how much data we generate, for example.
It might be that there are particular conditions we want to ensure are always created in the test data. For example, one I've already ensured happens is that at least one resource has zero tags attached to it, but if we think of more we can always extend this, and it should be much easier than manipulating ~1000 line JSON files.

$ docker-compose run --rm app ./manage.py init_data --help

usage: manage.py init_data [-h] [--clear-db] [--num-users NUM-USERS]
                           [--num-tags NUM-TAGS]
                           [--num-resources NUM-RESOURCES] [--version]
                           [-v {0,1,2,3}] [--settings SETTINGS]
                           [--pythonpath PYTHONPATH] [--traceback]
                           [--no-color] [--force-color]

Initialize the DB with some random fake data for testing and development

optional arguments:
  --clear-db            Clear existing data from the DB before creating test
                        data
  --num-users NUM-USERS
                        Number of `User` objects to create (default 10)
  --num-tags NUM-TAGS   Number of `Tag` objects to create (default 10)
  --num-resources NUM-RESOURCES
                        Number of `Resource` objects to create (default 10)
  -v {0,1,2,3}, --verbosity {0,1,2,3}
                        Verbosity level; 0=minimal output, 1=normal output,
                        2=verbose output, 3=very verbose output

[codecov]

Codecov Report

Merging #129 into master will increase coverage by 5.11%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master     #129      +/-   ##
==========================================
+ Coverage   76.33%   81.44%   +5.11%     
==========================================
  Files          28       29       +1     
  Lines         393      469      +76     
==========================================
+ Hits          300      382      +82     
+ Misses         93       87       -6     

Impacted Files	Coverage Δ
project/core/management/commands/init_data.py	83.56% <83.56%> (ø)
project/tagging/factories.py	100.00% <100.00%> (+100.00%)	⬆️
project/tagging/models.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c5eb5b6...c47e7ef. Read the comment docs.

[lpatmo]

Thanks so much for this! Learned a lot from your FactoryBoy setup too. Feel free to merge! :)