[WIP] feature/SCION HTTP endpoints and Webview

[martenwallewein]

Hey all,

The idea of this PR is to provide easy access to resources shared via SCION HTTP. It's first mentioned in #153. Unfortunately, a solution that provides access to these resources directly in the browser is not really practicable, mainly because SCION addresses could not be handled properly. So my current approach would be to

1. Allow the user to enter any SCION URL that can be accessed via SCION HTTP and display the results within the webapp
2. Collect some trending SCION HTTP resources that can be accessed directly (at the moment only our DVB-T2 live stream)

It looks like this (in a very basic version):

Hopefully, we can collect more resources and finally make them easily accessible via webapp.

At the moment, this is only a raw prototype and WIP, a lot of things still have to be done before getting this upstream:

• Replace the current used proxy with some forward proxy that supports multiple proxied connections
• Remove the NextProtos flag or make them configurable
• Clean up code and add styles to UI
• Add information to default tabs (like required player for the live stream)

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This change is