Merge pull request #7 from ciaranj/ash-calculus

Add support for the diffSeries function
Update the context menu lock/unlock behaviours

Have removed the titlebar's padlock, and put the unlock & lock options
directly onto the context menu.

Also stopped you from being able to select the context menu options when
they're visibily disabled (doh!)
Remove some old 'hoard related' eroneous scripts on installation.
Change the diffSeries function to pass null/undefined
if the initial value is null or undefined.
Add support for the movingAverage function

The moving average function charts the moving average of a metric
or metrics liset over a fixed number of   past points, or a time interval.

It does this by taking one metric or a wildcard seriesList followed by a
number of datapoints or a quoted string with a length of time like '1hour' or '5min'.

Calculating the average of the preceeding datapoints for each point on the graph.

All previous datapoints are set to 'None' at the beginning of the graph.