[#19] Remove ruby 2.0.0 from travis build matrix
Strongly simplify the default recipe

- no more "multi-users" setup
- no more group-trick to share write permissions
- no more symlink, sbt script is simply installed in a bin folder (like /usr/local/bin)

By the way:

- Fix #17
- Due to #20, '-batch' option is no more used
KISS: Except to install sbt script in an existing directory

If not done this way, we should add the ability to extend PATH environment variable (à la 'ark' LWRP).
Let's keep it simple for now...
[#17] Update sbt-extras script (with sbt 0.13.0 as default)
Very close to release 0.3, fix #18, #20