Feature request: Band and brick wall lines in charts

Add items to the Diet Calculator to display the ``band'' and the ``brick wall'' limits around the goal weight. (Suggested by Rob Campbell.)

Bug: Log navigation bar item disabled for historical log display

When displaying a log for other than the current month, the ``Log'' item in the navigation bar was highlighted and disabled, which prevented it from being clicked to display the current month. I added logic to test whether the current month is displayed (this, as the handling of the ``{\tt now}'' month specification, is presently based on UTC and needs to be reviewed with regard to {\tt tzoffset}). If the month displayed is not the current month, the ``Log'' item may now be clicked to jump to the current month. (Reported by Rob Campbell.)

Bug: trend carry-forward unit conversion in monthly chart

Further, when the log and display unit differed, the trend carry-forward (which is kept in the log unit) was not converted to the display unit, resulting in a vertical scale which squashed the actual data into a small part of the vertical extent---fixed.

Bug: diet plan unit conversion

Plotting of a ``flat-line'' diet plan in a monthly log failed to convert the kilogram quantity from the {\tt user} object into the display unit for the chart---fixed. (Reported by Rob Campbell.)