keyboard shortcuts won't fire with modifier keys

I had particular problems with Ctrl-N (open new window/tab)
interfering with N (go to next unread item). This change
disregards keyboard shortcuts if Alt, Shift, or Ctrl are used.
It also tries to disregard Win/Super/Meta, though this didn't
work for me in Firefox. Still, just the Ctrl is an improvement
for me.
Minor fix for Hello theme
Fix 404 errors for the Hello theme
Merge branch 'keyboard-shortcut-modifier-keys' of https://github.com/jarek/miniflux
Add contributor
Merge pull request #1 from fguillot/master

syncing with upstream master from github ui