layout: activity_main: Add Image Buttons

Add ImageButtons for Guests and dates
AndroidManifest: Add activities
layout: activity_add_guest: Add activity for adding guests
weddingapp: AddGuestActivity: Add Class for activity
weddingapp: GuestsActivity: Add activity for showing guests
res: menu: Add menus for the activities
layout: activity_guests: Add activity layout

Add activity layout for Adding guests
weddingapp: guests: DatabaseHandler: Add class for handling db