Update packaged JARs to use standard JarLauncher

Change CLI generated JARs to use the standard `JarLauncher` instead of
a custom `JarRunner`. The `PackagedSpringApplicationLauncher` is used
as the `Start-Class` which in turn calls `SpringApplication.run()`.
Exclude *.jar and *.groovy from generated JARs

Update `JarCommand` to exclude `**/*.groovy` and `**/*.jar` by default.
Polish CLI Jar generation
Pull-up duplicated code to Launcher