Add application frontend

[michael-markl]

This PR adds a structure which allows to create forms relatively easily. The PR includes

• an application form for the blue EAK using the most common entitlement type ("Berechtigungsgrund"): Work at Organization(s)
• auto-saving the application form (including files)
• Send GraphQL request to backend (including files)
• request gets processed successfully in the backend and is visible in the administration tool.

What's left:

• Make it a bit prettier
• [Application] Auto-Select Region  #624: Query regionId from PLZ of the antragsteller
• [Application] Add missing options for applications #628: Add options for JuLeiCa, Feuerwehrler, and goldene EAK
• [Application] Confirm with STMAS that application form is ready  #629: Check whether the form itself is complete (content wise)
• Validate applications in backend #622: Validate inputs and files in the backend
• Avoid vulnerable file uploads #329: Check files for malware (or sandboxing by browser?)
• [Application] Implement Organization-Verification PingPong #627: Add possibility for organizations to "verify" an application entitlement
• [Application] Make the application a standalone app #626: Make the application frontend a "standalone app" by e.g. adding an entry point in the administration folder.
• [Application] End Screen #625: Add screen for after the application is submitted.
• Properly handle dates as a separate JsonField (done in Validate applications in backend #622)

Sorry for the large PR, half of it is package-lock.json :)

[maxammann]

This is ready for review, right?

[michael-markl]

@maxammann yup

[michael-markl]

@maxammann You might want to have another look. If everything's okay, feel free to merge.

[maxammann]

Looks good!