dvp should provide a way to cleanup the build generated files

[fdrozdowski]

dvp build generates .dephix-compile direcotry, swagger generated python bindings and artifact.json as part of the build process (dvp build command). These files have to be deleted manually if user/plugin author wants to do a clean build or cleanup these files for some other reason. Adding a command like "dvp clean" or "dvp build --clean" would help.

(Source PYT-654)