- New configs for the graph's min and max hour.
  The previous method of calculating the min & max per day
  meant that the start & end of the graph represented a different
  time for each day's readings, making it hard to compare across days

- Changed calculation of X position in graph to use a 'minutes past earliest'
  concept - the earliest being a config option

- Render graphs with a Cairo gradient - looks much nicer

- Added vertical and horizontal lines from each X & Y axis label

- Fixed position of X & Y axis labels

- Summary and details datasheets are now next to each other - they don't
  take up much horizontal space. Added a vertical pane to hold these 2
  datasheets

- Added a horizontal pane to hold the graphs and datasheets

- Started decimal place formatting in datasheets - this has exposed
  some bugs :/