Add a button to open browser with PyDoc

Слиты nikitronn запросил слияние run_pydoc_button в master

Created by: portnov

  • visible under "Common Utils" in the N panel, only if "Developer mode" is enabled in addon preferences
  • Runs pydoc's server at localhost:8080 and opens web browser at this url; if pydoc is already running, just opens the browser.