[tei-council] TD section redo

Per ticket 1459 and Council's directive in Victoria, I have re-written the content model section of TD. Please read through both the prologue of * http://jenkins-paderborn.tei-c.org/job/TEIP5-dev/lastSuccessfulBuild/artifac... and its first subsection, * http://jenkins-paderborn.tei-c.org/job/TEIP5-dev/lastSuccessfulBuild/artifac... (they are both quite short: < 800 words of prose and 4 examples total) and let me know what you think. BTW, I note that in each example the link to the bibliography has migrated to the left. While politically I'm OK with that, aesthetically it's awful.