Implement test class ActivityPersistenceTest

[rgcv]

Issue by schimini Monday Apr 03, 2017 at 14:00 GMT _Originally opened as https://github.com/tecnico-softeng/es17al_01-project/issues/85_

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Dependencies:

1. ActivityProvider @rgcv - done in b0e5759

• [x] #57: Make ActivityProvider class persistent
• [x] #69: Make ActivityProvider's fields persistent
• [x] #92: Implement relation between DomainRoot and ActivityProvider

2. Activity @schimini - done in 4931b26

• [x] #55: Make Activity class persistent
• [x] #66: Make Activity's fields persistent
• [x] #84: Implement relation between ActivityProvider and Activity

3. ActivityOffer @schimini - done in 894b0e5

• [x] #56: Make ActivityOffer class persistent
• [x] #71: Make ActivityOffer's fields persistent
• [x] #88: Implement relation between Activity and ActivityOffer

4. Booking @rgcv - done in 36245c8

• [x] #58: Make Booking class persistent
• [x] #72: Make Booking's fields persistent
• [x] #90: Implement relation between ActivityOffer and Booking

Various commits should be associated with this issue, one per "persistence advancement"