Add WAdd WP_Query integration on init, not plugin loadP_Query integration on init, not plugin load

Switches the integration setup to fire on init, once WordPress is loaded and any potential theme filters have a chance to load.

Corrects an issue where it was not possible to use the ep_admin_wp_query_integration filter to enable admin side ES enhanced queries during an ajax callback (or possibly at all). Because the ep_admin_wp_query_integration filter was applied duting class instantiation (at plugin load), the returned value was always false.Switches the integration setup to fire on init, once WordPress is loaded and any potential theme filters have a chance to load.

Corrects an issue where it was not possible to use the ep_admin_wp_query_integration filter to enable admin side ES enhanced queries during an ajax callback (or possibly at all). Because the ep_admin_wp_query_integration filter was applied duting class instantiation (at plugin load), the returned value was always false.
Update test setup to call new integration function

Corrects test setup issue.
Merge branch 'bugfix/setup_wp_integration_on_init' into bugfix/set_up_wp_query_integration_on_onit
Merge pull request #178 from adamsilverstein/bugfix/set_up_wp_query_integration_on_onit

Add WP_Query integration on init, not plugin load