This updates the usage of integer types in code I wrote according to our new style guides.
Major changes:
* Use signed instead of unsigned integers in many places.
* C++ containers in blenlib use `int64_t` for size and indices now (instead of `uint`).
* Hash values for C++ containers are 64 bit wide now (instead of 32 bit).
I do hope that I broke no builds, but it is quite likely that some compiler reports
slightly different errors. Please let me know when there are any errors. If the fix
is small, feel free to commit it yourself.
I compiled successfully on linux with gcc and on windows.
This also introduces the `blender::nodes` namespace. Eventually,
we want to move most/all of the node implementation files into
this namespace.
The reason for this file-move is that the code fits much better
into the `nodes` directory than in the `blenkernel` directory.
