fixes #1531 - commentNavigator for IAmA
detect scroll position and update comment nav index accordingly for better commentnav when the mouse is involved
add keyboard navigation for comment navigator:

n - toggle navigator
shift+up arrow / shift+down arrow - navigate up/down
README: Remove sourcemap
nightMode: Use more reliable RESStorage check
Merge pull request #1535 from mc10/night-mode

nightMode: Use more reliable RESStorage check