.travis.yml: explicitly install Module::Build::Prereqs::FromCPANfile so build runs.
SafeData: update POD. Now users can use it.
WebAPI: POD and test: add only_statuses query parameter to GET statuses.json. Test is failing.
Main::PSGI, Main::PSGI::View: implement GET statuses.json only_statuses=1
t/WebAPI.t: check "error" field in erroneous cases.