Ability to see what is been shared

[IsmaelMartinez]

It will be great to be able to see what it is sharing.

Similar to what Skype does (small view in the corner).

Technically that requires the following:

1. Under https://github.com/IsmaelMartinez/teams-for-linux/tree/master/app/browser/desktopShare , create a new child view similar to the captureSelector.html. That will have a video tag for the video to stream to.
2. Modify the https://github.com/IsmaelMartinez/teams-for-linux/blob/master/app/browser/desktopShare/chromeApi.js#L9 to also stream the video to the page created in point 1. An example can be found in the desktop-capturer electron page https://electronjs.org/docs/api/desktop-capturer

Note, it might be needed to modify the captureSelector to also return the source type (desktop/screen).

[IsmaelMartinez]

I will be picking this one up tomorrow.

[IsmaelMartinez]

PR created. It does the basic. A couple of corner cases not handled at the moment (see the pr for more info).

I will not really have much time now for a couple of weeks, but wanted to push it up here as this might be an indirect fix for #61 .

I create this in a branch called feature/83