Split AKModel views into different files & introduce modular status page

• Move AKModel views into several subfiles to improve overview and resolve problems with circular imports
• Introduce new modular status page handling (widgets and views)
• Port main status page to new structure
• Move AK messages status page visualization to AKSubmission (therefore, they automatically do not show up when there is no possibility to create them)
• Introduce status widget for virtual rooms
• Fix timezone issue for rendering of AK messages on status page
• Adapt status page URL in several views and tests

This lays the foundation for #105