Progressive Web App

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Add a button to the member page to install Hacklab progressive web application (PWA). This is mostly just some lab specific static content such as application manifest file and application assets, but might need some additional endpoints to the API:

• Registering of application access key (public key or token) to the member data.
• Get certificate (signed with real crypto or just some token) about if the membership is active, state of key membership etc. basic info. Used for key system in labs which have on-line door control. Jyväskylä: planned, Tampere: possible.

Requires a mock demo first to check what features are required from Mulysa. The actual PWA can be developed as a separate project and probably doesn't need to be included in the Mulysa project at all.