Nextcloud integration

[longsleep]

Similar to the Nextcloud issue nextcloud/server#828 this issue tries to break down Nextcloud integration in work packages.

• Remove top bar, integrate call control with notifications
• Bootstrap 3 theme for buttons, headers and input which matches the Nextcloud style
• Further Nextcloud style harmonizing
• Make Spreed.ME settings available as Nextcloud settings – Allow to configure the app via web interface #39
• Client and server side session resumption and keep-alive, including client-side and server-side queue
• Call resumption support after navigation (auto hold / resume)
• Web client build target to support Nextcloud without Go backend. / maybe split out the web client
• Define and implement Web client API for Nextcloud UI integration from other apps

Please comment if i missed something.

[JSoko]

Features witch would be also nice to have in Spreed.ME under Nextcloud too:

• Locking a room How to lock the room? spreed-webrtc#239
• session recording Add support for meeting recording spreed-webrtc#331
• Using Spreed Desktop for invited People who are not Nextcloud Users Using Spreed Desktop for My Own Spreed WebRTC spreed-webrtc#342
• integration of sip voip Support SIP with a kind of SIP Gateway? spreed-webrtc#297

[enoch85]

• Make it possible to generate a new Shared Secret and SpreedMe WebRTC config via CLI

This is to make it possible to fully automate the install in the Nextcloud VM.

[leonklingele]

We now have https://github.com/nextcloud/spreed