When cancelling the prompt to install the extension, instead of
treating it as a generic error treat is as the cancel extension
error. This allows existing logic to trigger that will not show
an error message on cancel.

* fix(SS): Set min and max frame rate to 5

* fix(SS): Set min and max frame rate for the new GUM flow.

* feat(ss_framerate): Add config option for min/max frame rate.

* doc(RTCUtils): Fix params format.

* fix(SS_framerate): Don't pass undefined constraints.

* fix(SS_constraints): Handle  chromeMediaSourceId === undefined.

* log: Logs when analytics are disposed, drops events early.

* fix: Adds a missing parameter to a function call.

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

To install the chrome webstore extension, the user must already have installed "Download Chrome Extension". On missing extension we open a popup window which allows the user to add the extension and then install it.

ESLint 4.8.0 discovers a lot of error related to formatting. While I
tried to fix as many of them as possible, a portion of them actually go
against our coding style. In such a case, I've disabled the indent rule
which effectively leaves it as it was before ESLint 4.8.0.

@paweldomas said the typo should likely remain because it matches a typo
in Chrome.

Will trigger external installation also for sites that are not the main
whitelisted domain. This allows to reuse one extension for many sites
(they still have to be on the whitelist, but only one can be "main").

Will not crash, but delay requests if arrive, before the initialization
process is done (there is no way to tell that really).

CHROME_EXTENSION_USER_GESTURE_REQUIRED will be triggered if
the extension installation fails, because the request to get desktop
stream did not originate in user gesture handler (a button click for
example).

* feat: add 'disableDesktopSharing' option

* ref(ScreenObtainer): simplify init

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

#416