Couple site tweaks
[#1091] Rewrite ArchetypeBuilder in Java
[#1091] Add hello-world archetype
[#1091] Add hello-world example for testing archetype generation
[#1091] Add tests for archetype creation + fixes to the process
[#1091] Should we use 2 or 4 spaces for XMLs?
Scaled screenshots down a bit so they are less big in the docs
Polished
Moved spring-boot quickstarts to a sub dir.
spring-boot archetypes improved.
[#1091] Added the quickstart/spring-boot dir to the archetype builder. @Ignore a failing test on osx.