fix bug: Invalid face reference: python-cell [xxx times]
make mode-line lighter shorter
add support for indented cell

This closes issue https://github.com/thisch/python-cell.el/issues/3
enhancement: print cell header line in python shell when sending
fix bug when trying to get cell header line but beginning-of-buffer has no such header
activate python shell buffer after sending cell
properly get shell buffer name when activating shell buffer
add a 'noactivate' arg to 'python-shell-send-cell'
avoid 'Mark set' after auto scrolling to end of shell buffer