Add "frontend" target to default build target

What does this MR do?

Add the frontend target to the default build target. This means that calling make all in this module and downstream modules builds the frontend as well.

Why was this MR needed?

Users (like me) might not expect that targets required for an application might not be built through make all. With currently no documentation about which targets to build, it is safest to simply add the frontend to the default build target.

Open questions

Might there be a particular reason why the frontend target was not added to the default build target? If so, we'll have to discuss that, of course 😉