This just gets the plumbing in place with some basic categorization for
callgraph information. The real work of categorizing by nick/symbol still
needs to be done (some can be copied from SysprofCategoryIcon).
This also adds a property and getter for SysprofCallgraphFrame which will
expose the node's category to the UI code.
This brings together the two libraries back into one now that the whole
design is pretty well sorted out. They depend on roughly the same libraries
anyway and it's way easier of the single library can both read and write
the capture files (along with bringing in libsysprof-capture symbols in
a single place).
