Fixing EVENT-33
 - do a null check when looking to see which blocks originally went with a page
Adding lots of javadoc and inline comments
 - refactored methods to proper classes
   - method that converts a `List<Page>` to `List<PageEntity>` moved to `Page`
   - method that converts a `List<Block>` to `List<BlockEntity>` moved to `Block`
   - utilize `List.contains()` to check and see if a `Page` or `Block` is new, instead of `Set` comparisons
FIXME was actually incorrect.

the `PageService` does delete `BlockEntity`s that belong to its `PageEntity` before deleting the `BlockEntity`
Update UpdateConferenceProcess.java

fix typo
Merge pull request #211 from CruGlobal/EVENT-33

Fixing EVENT-33