Update docs to showcase session tracking and es6 syntax

[niemyjski]

We need to update the samples to show how to use the client in es6 (import syntax) and add a angular4 sample :). The closest sample we have is our typescript sample: https://github.com/exceptionless/Exceptionless.JavaScript/blob/master/example/TypeScript/index.ts

Here is the old way that needs to be converted to es6 import

         var config = exceptionless.ExceptionlessClient.default.config;
         client.config.useLocalStorage();
         client.config.setVersion(‘1.2.3’);
         client.config.setUserIdentity(‘id’, ‘friendlyname’);
         client.config.useSessions();
         client.createFeatureUsage(location.pathname || ‘/’).addTags(‘UI’).submit();