Testlib request methods

[will-moore]

What this PR does

Cleanup of omeroweb.testlib Django client request methods, based on https://trello.com/c/flvJ728g/31-web-api-tests-to-include-csrf.

Previously we've had a number of testlib methods such as:

_post_response
_post_response_json
_csrf_post_response
_csrf_post_response_json
_csrf_post_json
_csrf_put_json
_delete_response
_csrf_delete_response
_csrf_delete_response_json
_get_response
_csrf_get_response
_get_response_json

These try to cover a matrix of:

• GET, POST, PUT, DELETE
• With or with CSRF tokens
• POST data as query string or JSON content
• Handling response as text or JSON

These are replaced by a smaller number of methods.
For all POST, PUT & DELETE we first test without CSRF (check for 403 response) then with CSRF.

(This means that all the test_api_* tests are now being tested for CSRF checks, as per trello card above).

get: GET without CSRF (parameter for CSRF option)
get_json: as above, but handles JSON response
post: POST - data encoded in query string
post_json: POST, encodes data as JSON and handles JSON response
put_json: PUT, encodes data as JSON and handles JSON response
delete_json: DELETE, encodes data as JSON and handles JSON response

csrf_response: underlying helper method is available if you want to do POST/PUT/DELETE without doing the CSRF test.

All ```Omeroweb/test/integration``` tests have been updated to use new methods.
Original methods above are marked with deprecation warnings.

Testing this PR

1. Tests should be green.

[jburel]

missing method argument

[jburel]

Maybe indicate the one to use in the message

[mtbc]

Would you mind temporarily excluding this so we can try to get #5349 in?

[will-moore]

@mtbc Added exclude label to description.

[jburel]

@will-moore could you remove the exclude label and fix the merge conflict
now that #5349 is in

[will-moore]

Travis failure: "This job ran on our Trusty environment, which is gradually becoming our default Linux environment. You can add dist: precise in your .travis.yml file to continue using Precise."

[jburel]

@will-moore could you roll back your latest commit?
I am adjusting the travis file in gh-5409
so we can update pytables (see gh-5407)

[jburel]

Thanks for updating message
Tests are passing
Merging so we can unlock other PRs