Test/featuretestcase

[jim-parry]

• added 'patch' to allowed HTTP verbs in RouteCollection
• added resetRoutes() in RouteCollection, to support FeatureTestCase
• added output capturing to FeatureTestCase::call
• added more methods to tests/_support/Controllers/Popcorn, to generate all the different kinds of responses
• added note to testing/features in user guide

Related to #1767, #1692 & possibly #1697
Closes #1767

[jim-parry]

Three SQLite3 tests are failing, and there are some warnings for SQLite3 too.
I don't see these being related to the current PR, though they pass travis-ci for other PRs.
This should be ready to go, as far as I can tell.

[lonnieezell]

Doesn't look like those tests are affected by anything you did. They seem to be missing a $refresh = true or similar on those test classes.

[jim-parry]

I think there is something screwy with travis-ci.
I re-ran the test suite that failed, and now three different tests fail - Validation ones.
It seems that the db_user table is sometimes there for SQLite3, and sometimes not.