Added dependency on Culturefeed Search UI to the Culturefeed Agenda module.

After enabling culturefeed_agenda and visiting agenda/search I got the following error:

Fatal error: Call to undefined function _culturefeed_search_ui_get_active_search_page() in culturefeed/culturefeed_agenda/culturefeed_agenda.module on line 438

culturefeed_agenda depends on culturefeed_search_ui.