Use new Flags template for new Deletion flags
* src/global.h (DeletionFlags): Rename to... (DeletionFlag): ...this. Change underlying type to unsigned int. Remove UseDefaults enum value. (DeletionFlags): New type for combinations of DeletionFlag. Define enum flag operators for this type. (operator|): Remove overload for DeletionFlags. * src/context.cpp (Context::deleteKey): Adapt to above changes.
The enum value UseDefaults (= 0) is removed because it can now be
represented by default-constructed DeletionFlags.