Have you tried or considered adding a Maven Jetty plugin for faster development? Instead of having to recompile and redeploy the app for front-end changes you could just refresh your browser and see the changes immediately.
<plugin>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-maven-plugin</artifactId>
<version>9.2.11-SNAPSHOT</version>
</plugin>
Unfortunately, since your app doesn't have a web.xml and initializes it through code, the Maven Jetty plugin doesn't work unless you have Jetty 9 (Servlet 3.0) but for the life of me I can't seem to build the Jetty 9 Maven plugin because I can't seem to find the right repository that has it.
Alternatively, do you happen to have a web.xml that can be used instead of the WebAppInitializer?