Rename doc-* targets to be less generic

Now that there are a lot of other documentation targets as well, rename
the targets that generate Doxygen documentation to doxygen-*.
Also, rename the doc-check target to source-check, since it has evolved
to more than just a Doxygen documentation checker.

There is some backwards-compatibility glue for Jenkins that expects to
execute the doc-check target with the old name, but otherwise this
change should only be visible to those few developers that may generate
the Doxygen documentation themselves or run the check-source target.

Change-Id: If69b4becc2bdc17899fa17ffd12ea1516133457b