Added geolocation (new); surfaced appcache and webaudio samples

src/site/samples/geolocation/index.markdown

+---
+layout: default
+title: A Basic Geolocation Example
+live_example_url: example/index.html
+header:
+  css: ["/samples/samples.css"]
+---
+
+## {{ page.title }}
+
+The Geolocation API lets you track a user's location. The API is
+device agnostic; the underlying mechanism might be via GPS,
+wifi, or simply asking the user to enter their location manually. Since
+these lookups can take some time, the API is asynchronous, and you
+pass it a callback method whenever you request a location.
+
+The Trip Meter example displays the user's initial location, and it
+tracks the distance the user has travelled since the page was loaded.
+
+You can open the example in Dart Editor and run it by clicking `index.html`.
+
+<iframe class="running-app-frame"
+        style="height:300px;width:100%;"
+        src="{{page.live_example_url}}">
+</iframe>
+
+Read the
+[source](https://github.com/dart-lang/dart-samples/tree/master/web/html5/geolocation/trip_meter).
+
+See all [samples](/samples/).