Residents of a Brooklyn street remained stunned and baffled in the aftermath of an apparent murder-suicide police believe was committed by a lifelong resident loved by all. On Wednesday, Jason Jackson and his girlfriend Olga Kirshenbaum, both 34, were both found dead in their apartment on Second Street near Fifth Avenue in Park Slope, cops said. Kirshenbaum, nicknamed “the Money Whisperer” by her clients, was an established author and owner of Rags to Riches Consulting, where she provided financial advice to artists and creatives, according to her website. Both victims had been shot in the hea…