Rename documentation directories to fix devhelp

It appears that devhelp only finds module docs if the name of the .devhelp2 file corresponds with the directory it's in.

We previously installed these:

/usr/share/gtk-doc/html/libtracker-sparql3/libtracker-sparql.devhelp2
/usr/share/gtk-doc/html/tracker3-nepomuk/ontology.devhelp2

After this commit, we install in a way which will work as expected with devhelp:

/usr/share/gtk-doc/html/libtracker-sparql-3/libtracker-sparql-3.devhelp2
/usr/share/gtk-doc/html/ontology-3/ontology-3.devhelp2