Documentation of cubits, models and widgets

[Scarletto]

The PR with documentation requested in #91.
Please feel free to add or change things to this branch!
Move to "In progress" what you are working on.
Check off and move back what is done.

In progress

• placeholder

Cubits

• album_cubit
• album_list_cubit
• calendar_cubit
• event_admin_cubit
• event_cubit
• food_admin_cubit
• food_cubit
• full_member_cubit
• group_cubit
• groups_cubit
• liked_photos_cubit
• list_state
• mark_present_cubit
• member_cubit
• member_list_cubit
• payment_user_cubit
• registration_fields_cubit
• sales_order_cubit
• setting_cubit
• theme_cubit
• welcome_cubit

Models

• album
• device
• event_registration
• event
• food_event
• food_order
• frontpage_article
• group
• list_response
• member
• payable
• payment_user
• payment
• photo
• product
• push_notification_category
• registration_field
• sales_order
• slide

Widgets

• album_tile
• app_bar
• cached_image
• error_center
• error_scroll_view
• event_detail_card
• gallery
• group_tile
• mark_present_dialog
• member_tile
• menu_drawer
• pay_tile
• photo_tile
• push_notification_dialog
• push_notification_overlay
• sales_order_dialog
• tpay_button

[JAicewizard]

Before you start too much on this, I want to combine and rework the list cubits to share a lot more code. It might be nice to wait with documenting them untill thats done (it might take a while tho)