+ raw pointers were bug-prone, especially as there was no standard approach as to where delete them (see: database.cpp)
+ now all pointers to DatabaseQuery are shared_ptrs
+ added reset() in all places where we free a part of query anyway, so that the caller can at least check if the pointer passed to callee is still valid after return
+ added missing base_handler include to dbinquirer and fixed base_handler's includes