initialize invites

Invites model,controller and views are initialized.

add datepicker and selectize in invites#new

calender is added for end date field and selectize is added for emails field to allow multiple emails in field

app/models/conference.rb

@@ -33,6 +33,7 @@ class Conference < ApplicationRecord
   has_many :resources, dependent: :destroy
   has_many :booths, dependent: :destroy
   has_many :confirmed_booths, -> { where(state: 'confirmed') }, class_name: 'Booth'
+  has_many :invites, dependent: :destroy
 
   has_many :lodgings, dependent: :destroy
   has_many :registrations, dependent: :destroy

app/models/invite.rb

@@ -0,0 +1,8 @@
+class Invite < ApplicationRecord
+  attr_accessor :emails
+  belongs_to :conference
+
+  validates :end_date, presence: true
+  validates :invite_for, presence: true
+  validates :user_id, presence: true, uniqueness: { scope: [:invite_for, :conference_id] }
+end