adds notification sending from dse_allocator to messenger, and creation/insertion of the notifications in dse_messenger

adds new DTOs for notifications
adds DAO for dse_messenger

lots of cleanups and fixes
adds additional "AND Type" clause into findFreeOpSlots query in dse_allocator

(now correctly finds op_slots with the specified type)

adds UI DAO
(so far AdminController and DoctorController refactored, rest to do)

adds debug view (home) in dse_messenger to see notifications in database

general cleanups and refactoring