fix(controller): store limit fields on config

Having a separate "Limit" domain object was getting in our way, when
really it represents just an extension of a Config. This moves the
two JSON fields "cpu" and "memory" to Config and does away with Limit.
fix(controller): specify dicts as defaults and guard against old errors

We should have been initializing our JSONFields with dict objects, not
strings. Also upgrading from a slightly earlier version of Deis to this
change could hit a JSON encoding error, so catch that and use the chance
to clean up the data. Also reverted the unnecessary workaround of
subclassing JSONField.
test(docs): add a `make test` target
docs(community): add policy on bounties
Merge pull request #1630 from mboersma/1613-limit-is-config

fix(controller): store limit fields on config
Merge pull request #1650 from gabrtv/bounty-policy

docs(community): add policy on open source bounties
chore(controller): update djangorestframework to 2.3.14

Several months of cleanup and bug fixes to a core Deis library:
https://github.com/tomchristie/django-rest-framework/compare/2.3.13...2.3.14
fix(builder): don't reload cedarish if its already loaded

Ref #1643

Also add log messages
Merge pull request #1645 from deis/builder/dont-reload-cedarish

fix(builder): don't reload cedarish if it's already loaded
Merge pull request #1648 from mboersma/1646-docs-make-test

test(docs): add a `make test` target
Merge pull request #1586 from mboersma/update-django-rest

chore(controller): update djangorestframework to 2.3.14
fix(controller): validate Cluster.hosts field as comma-separated hostnames