Move all user-facing strings to a new module.

This should eventually, hopefully, allow translating
the software to other languages. Of course, the strings
in the static HTML are not yet included.
Don't let auto-scrolling fire scroll() (fixes #9)

The biggest problem with a0152370541f3865ca49f116bcdeda5dfe39fd21
is that scroll() doesn't only fire on manual scrolling, but
but also when we scroll automatically. Therefore, inadequate
autoscrolling can still cause it to turn itself off.

This patch makes sure that checkAutoscroll ignores events
triggered by automatic scrolling, so autoscrolling cannot disable
itself.

Also, autoscrolling now doesn't turn off until a certain portion
of the screen has been scrolled up (currently a third). This should
also prevent weird problems when the pixel heights don't seem to add
up perfectly, and even scrolling to the bottom won't turn it back on.