new Renderer implementation

The new API should provide the necessary functions to render a call and preview. Moreover, this should also fix the issue when a crash occurs when the preview is open.

Patch

https://gerrit-ring.savoirfairelinux.com/c/ring-lrc/+/10319

mentioned in issue #394 (closed)

changed milestone to %New media API

assigned to @sblin

changed title from MediaModel implementation to new Renderer implementation

changed the description

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changed time estimate to 2d

added 2d of time spent at 2018-11-11

changed the description

closed