Standard audio constraints need to be passed to gUM for audio input device selection
to work properly on Safari.
Safari doesn't support permissions query, add a workaround for that.

* fix(permissions): remove space from requesting camera

Chrome errors on querying permissions with "camera "
because it does not match an expected enum.

* fix(permissions): check value of returned PermissionStatus

A permissions query returns an object with a status/status
of whether or not permission has been granted. Check that
value in addition to the existence of the object.

* fix(permissions): prevent permission being set to undefined

* ref(permissions): move permissions strings to constants

Use the W3C Permissions API where possible. At the time of this writing this is
supported in Chrome >= 64.

In order to include browser capabilities in RTCBrowserType I needed to
refactor RTCBrowserType.

Webpack 2 defines module.exports as a read-only property in ES6 modules.

For audio previewing, some browsers cannot have multiple local
audio streams at once. For audio output previewing, local
stats need to be collected to detect changes in volume level.

Pull Request #435

Our JSHint configuration is not extensive and we have excluded multiple
files from linting. Additionally, we have seen JSHint to be unable to
parse newer ECMAScript features such as the object spread operator
(proposal).

On the other hand, we have seen ESLint to beautifully work on React and
React Native source code in addition to ES2015 and later. Introduce
ESLint alongside JSHint as an intermediate step to eventually switching
from JSHint to ESLint.

As our source code does not fully follow even the JSHint rules we have,
it is very difficult to introduce ESLint with many rules. At the
beginning, introduce it with as little rules as possible. Morever,
ESLint is able to automatically fix certain rule offenders so once we
have ESLint merged we can incrementally add new rules while keeping our
commits' modification on as little subjects as possible.

On Safari/IE we have to wait until the WebRTC stack is
initialized in case the plugin is being installed for
the first time.

Fix non-ASCII letter in Statistics.sendActiveDeviceListEvent() method

Needs an additional check for available devices after merging https://github.com/jitsi/lib-jitsi-meet/pull/139.