Additional customised graph smoothing, zoom etc

This release adds the ability on the graph screen to choose custom smoothing, expo and zoom settings for each graph field.

By default, the standard logger would setup smoothing, expo and zoom factor automatically; now you can just choose the settings you want to look at.

For the Smoothing Field, the default of 30% matches the standard logger for most fields except for motors, which was smoothed 50%. 0% is no smoothing and represents the raw data directly, 100% is maximum smoothing.

For the Expo setting, this was different for each field, 25% being the default expo for gyros. The expo function exaggerates the scale at the centre line; a value of 100% is a linear scale.

The Zoom setting is self explanatory, 100% is normal, 200% zooms the chart in vertically. Warning, as you zoom in, the chart pen can go outside of the chart limits (overlapping other graphs).