Implementing global inputs running on all nodes

Introducing InputState class which holds the current runtime state of an
input.
Added proper displaying of new notification classes for failing inputs
and nodes without any running inputs.
Supporting launch/management of global inputs including extractors and
static fields. Using master node to direct api calls against in case of
global inputs.

Fixes #343
Fixes #251
Merge git://github.com/Graylog2/graylog2-web-interface into develop