Add ability to create sitemap shortcuts (#1357)

mobile/src/main/AndroidManifest.xml

.../src/main/java/org/openhab/habdroid/model/LinkedPage.java

...e/src/main/java/org/openhab/habdroid/ui/MainActivity.java

.../src/main/java/org/openhab/habdroid/ui/WidgetAdapter.java

...main/java/org/openhab/habdroid/ui/WidgetListFragment.java

...a/org/openhab/habdroid/ui/activity/ContentController.java

.../main/java/org/openhab/habdroid/util/AsyncHttpClient.java

...e/src/main/java/org/openhab/habdroid/util/HttpClient.java

...c/main/java/org/openhab/habdroid/util/SyncHttpClient.java

mobile/src/main/java/org/openhab/habdroid/util/Util.java

mobile/src/main/res/values/strings.xml