CRM-13738 fix - Activity Report fails if filtering on any contact

The PR consist of following fixes:

1) Previously Activity fails if filters on any three contact in specific (assignee,target,source) as because where clause is not being handled in recent changes of CRM-13467, current changes handles that.
2) In report Activity time and type are set defaults so whenever we unselect these attribute from 'Display Columns' it throws DB error as unknown column in orderBy. Fixed it by making those fields required.
3) Last but not the least indention fix.