Bug 871127 - [dialer] cannot make a second call through dialer

- Refactor the CSS for the icons
- Add a place-new-call button
- Show the dialer toolbar with a smaller height
- New tests for modified functions
Merge pull request #11931 from Rik/second-call-871127

Bug 871127 - [dialer] cannot make a second call through dialer r=etienne