Restrict new windows in replay + improved service worker loading + better error messages (#126)

* embeds:
- support target rewriting with named iframe as per webrecorder/wombat#94
- refactor sw init: detect additional errors, such as CORS issues in nested iframes
- support cross-origin replaybase for embeds
- add 'requirecrossoriginiframe' to restrict embed to only be loaded in subdomain iframes, otherwise showing
- rename noSandbox -> sandbox, not enabled by default

init: set appName on service worker init
docs:
- add example embed to embedding doc
- update docs for noSandbox -> sandbox
- add warning if deprecated 'noSandbox' flag is used, explaining that it is now deprecated
- update embedding and CHANGES.md with latest features
- add tweet-example.wacz
- add embed.html to test embeds

bump to 1.7.0-beta.1

embed.html

@@ -0,0 +1,15 @@
+<html>
+<head>
+<script src="ui.js"></script>
+<style>
+body {
+  background-color: lightgrey;
+}
+</style>
+</head>
+<body>
+
+<replay-web-page replaybase="./" embed="replay-with-info" src="./docs/assets/tweet-example.wacz" url="page:0"></replay-web-page>
+
+</body>
+</html>