added events, confirmed events and events with comments export features with xlsx, pdf and csv format

app/views/admin/events/index.csv.haml

@@ -1,25 +0,0 @@
-- headers = ['Event ID',
-             'Title',
-             'Abstract',
-             'Start time',
-             'Submitter',
-             'Speaker',
-             'Event Type',
-             'Track',
-             'Difficulty Level',
-             'Room',
-             'State']
-= CSV.generate_line headers
-- @events.each do |event|
-  = CSV.generate_line([event.id, event.title, event.abstract, event.time,
-                       event.submitter.name, event.speaker_names, event.event_type.title,
-                       (event.track.present? ? event.track.name : 'nil'),
-                       (event.difficulty_level.present? ? event.difficulty_level.title : 'nil'),
-                       (event.room.present? ? event.room.name : 'nil'), event.state])
-
-= CSV.generate_line [nil]
-- headers = ['Comment ID', 'Event Title', 'Body', 'User Name']
-= CSV.generate_line headers
-- @events.each do |event|
-  - event.root_comments.each do |comment|
-    = CSV.generate_line([comment.id, event.title, comment.body, comment.user.name])