Regarding your first question, the Android L skin is called 'material' and 'materialblack' or 'material-dark' and 'material-light' depending on your Kendo UI version. You can check this out in the Kendo UI Application documentation
. You can check the version of Kendo UI you are using in your app by opening any Kendo UI file. The version is at the top.
To your second question, the answer is no - AppBuilder does not update Kendo UI automatically. It is advisable to thoroughly test your app should you decide to update a framework library as Kendo UI Mobile. We always aim to not introduce breaking changes, but it's still possible that some of your functionality breaks. This is the main reason AppBuilder does not update Kendo UI libraries automatically. However, there is an easy way to change Kendo UI packages in your app. Right click on your project -> Manage Packages -> Kendo UI. Kendo UI Core contains Kendo UI Mobile only and Kendo UI Professional adds the DataViz mobile features. Simply choose a version and click Install. This will replace the contents of your kendo folder with the new version.
Let me know if this information helps and don't hesitate to ask should you have more questions.