Researchers and hospital executives walked away from a gathering at the White House with renewed vigor and morale after President Barack Obama announced a$215 million plan to grow cancer therapies and understanding in medicine tailored to a person's genetics. The funding, which still needs Congressional approval, would accelerate work ongoing in many of Boston's top hospitals and biotechnology firms, from Dana-Farber Cancer Institute's to Partners HealthCare's, to hundreds of Cambridge biotechs, breaking open once-siloed sources of information, and giving researchers the funding necessary to find new cures for cancer.