This doesn't yet render things, but it starts to get the plumbing in place
so that we can create a custom row type and then consume the marks
catalog from SysprofDocument eventually.
This is a raw view of the marks in a session which should help for just
finding the information you care about when the visual model is too
cumbersome or lacks searching capabilities.
This is ultimately to replace libsysprof-ui, and will focus on the display
of capture files. Recording will be left to the sysprof application in
terms of UI, and other applications like IDEs will use the
libsysprof-profile API directly along with libsysprof-gtk for visualizing.
