Remove TieredStopAtLevel option

Not supported on jdk 6
Update to pallet 0.8.0-beta.5
Updated project.clj, release notes and readme for 0.6.0-beta.7
Merge branch 'release/0.6.0-beta.7'
Merge tag '0.6.0-beta.7' into develop

pallet-lein-0.6.0-beta.7
Updated version for next release cycle