Added basic Favor class
Added TimeTransaction class with basic functionality
Added (incomplete) MemoryTimeManager
Added TimeBucket as a concept
Removed MemoryTimeBucket and Added the real, ActiveRecord supported, one
Added validation support to StaleObjectError throwed by TimeBucket class
Added two rake tasks to execute slow and fast tests
Merge pull request #13 from jd-erreape/add_basic_favor_classes

[WFA] Add basic favor and time transaction (exchange) classes