Blender Git Loki

Added back defines of "opcodes" for opearation nodes

These are essentially identifiers we can use for quickly checking or searching
for particular types of operation nodes from a component, without resorting
to dynamically building identifier strings or other crazy stuff like that.

* Unlike in the past, these are stored on the OperationDepsNodes themselves.

* Not all operations need to have an identifier defined. Only those operations
which are very common or important must have one. All others can simply
reuse the generic "DEG_OPCODE_OPERATION" with a suitable string

* These are defined in a separate header, which is designed to be used like UI_icons.h
to create a set of printable string ID's for nicer debug printing