Support for plugging Boombox into Membrane pipelines

[mat-hek]

The goals are the following:

• create a way of extending Boombox capabilities without increasing complexity and entry level for the Boombox itself
• simplify Membrane pipelines by replacing parts of them with Boombox

The solution can be to change Boombox implementation from pipeline to bin and create a thin pipeline wrapper over that bin to preserve current API. Then, the bin can be plugged into a Membrane pipeline. We should focus on ease of linking the bin and make sure we don't introduce too much overhead in the connection between Boombox and the rest of the pipeline