Adds failing test for stage updates no replacing old configuration in stage groups
Replaces the StageGroup stages set with a map to ensure only one configuration per stage is stored
Ensures StageGroup getters return unmodifiable copies of it's map
Adds a getSize method to StageGroup and uses it instead of getStages().size()
Adds debug logging of result when writing properties
Adds isEmpty() method to StageGroup
Brings test dependencies up to date

junit to 4.11 and mockito to 1.9.5
Removes Java 7-specific method
Merge pull request #262 from laserval/fix-259-java6-compilation-error

Fix for #259: Removes Java 7-specific constructor
Merge pull request #261 from Nycander/fix-junit-dep

Brings test dependencies up to date
Merge pull request #231 from laserval/stage-update-fix

Fixes one cause of #168