When looking for a new home to replace its cramped office condo in a suburban strip mall far from downtown Austin, Humanities Texas director, Michael Gillette, liked the location of the Texas Oil Company building, just blocks from the state capitoI.   But while it had abundant space, access to parking, and a fair price, it was ugly: its cheap stucco façade was only surpassed by a bland interior.  On an inside wall was a historic black-and-white photo of a spectacular old home and it turned out to be still there on the site, a brick mansion entombed beneath thick layers of stucco.