PLT-427 - Periodic schedules

Add data structures and logic to generate schedules
Move Frequency and RollConvention
Add StubConvention
PLT-427 - Periodic schedules

Fixup from PR
PLT-427 - Periodic schedules

Fixup from PR
Merge pull request #18 from OpenGamma/topic/PLT-427

PLT-427 - Periodic schedules