Make RRD writes thread-safe and error non-fatal

Change the way RRD counters are updated in order to enable statistics in case
several workers are spawned.

Do not crash if an RRD write failed due to a duplicate timestamp.
Add Bonnières station and turn some E's into É's

Some stations have names containing capital E's that actually should have an
acute accent on them.
Add Redis support

Enable caching using a Redis backend.  This backend provides a shared cache
which automatically invalidates cache entries after a certain time.

Use of Redis is optional and controllable using the use_redis option; this to
make the Redis dependency optional.
Merge 'redis' branch into 'default'
Remove useless console.log() statement
Improve autocompletion behavior when blurring text box

Add a proper onblur handler for the station selection text box.  This handler
returns the text box to the original station name and hides the autocompletion
drop-down menu.

This handler is also connected to the Escape key.
Autocompletion: fix mouse click handler

Adding the "autocomplete reset" feature somehow broke mouse click events.
Work around that by taking the reset feature out of onblur and catch it
directly when clicking outside the drop-down menu or by pressing Escape.
Update some station names and add line information for Bréval