PURCHASE AND SALE CONTRACT AMONG ROYAL CREST ESTATES (MARLBORO), L.L.C. AIMCO ROYAL CREST – NASHUA, L.L.C. AIMCO WARWICK, L.L.C. WATERFORD VILLAGE, L.L.C. AIMCO WEXFORD VILLAGE, L.L.C. AIMCO WEXFORD VILLAGE II, L.L.C. AS SELLERS AND HGI ACQUISITONS,...