[app] Java runtime manager

[at15]

Need to look at reika's java implementation, and found out I don't have jdk installed on my os.
It can also be used as a base for managing other runtime packages, like node (without using nvm).

• install oracle jdk from tar
  • might automate the download process
  • use update alternative on ubuntu ... require sudo ...

Ref

• https://github.com/shyiko/jabba 399 star go based, modeled after nvm
• https://github.com/gcuisinier/jenv 1.8k star pure bash
• https://github.com/linux-china/jenv 506 star, pure-bash