Playing on permission system.
Added authorization service.
Revised authorization service and role store.
Refactored and commented.
Added tenant filter and permission grant classes.
Refactored and renamed classes.
Working on user role management.
Removed navigation properties from UserRole entity.
Added consts to AbpUser and fixed user store.
Refactored classes, namespaces. Also adapted to ABP changes.
Updated upon changes on ABP framework.
Changed AbpZeroDbContext to receive connection string from inheritor. Fixed #5