fix unescaped '+' in query params

fixes #223
ported Api tests to new class
use correct error message
add asking all nodes to ApiClient

the remaining missing functionality to ApiClient was to execute requests against all graylog2 nodes in parallel
add test cases
update to play 2.1.4 fixed #199
I always forget travis.yml fixes #199
Merge branch 'play' into timerangeselector

Conflicts:
	app/lib/ApiClient.java