Custom summary bandwidth stats charts.

Meant to replace the vnstati generated summary chart. Provides
information on today, yesterday, this month, last month, and total
bandwidth usage.

Note that no precautions were taken for the case where vnstat is newly
installed and so has no data for yesterday/last month. I didn't want to
wipe my stats to test it. Will revisit later when I move to a new
seedbox.

I notice that the daily stats from vnstati were calculated based on the
time that the computer was actually on. Can't figure out how they got
that from the data available in dumpdb, so maybe it's some extra data
they store in the database that isn't available?

Using AwesomeChart to generate the chart graphics in javascript.
Downside is that because it's using html5's canvas, you have to state
fixed width & height for the canvas. Also had to hardcode colours in
javascript for the charts.