feat(toolbox): implement buttons using ToolboxItem
Currently the following are implemented:
- AudioMuteButton
- HangupButton
- VideoMuteButton
In order to implement these new buttons a new abstract class was introduced,
which abstracts the ToolboxItem into a button with enough hooks so a stateful
and a stateless version of it can be created.
This patch only adds the stateful implementation of the aforementioned buttons.