Added Javadoc for androidplot
Some formatting changes to the graphs

* values are shown in oldest to most recent order (left to right)
* times are shown on the x axis
* title is set to the name of the station
* legend is no longer visible
no need to create an array
fixed formatting of the x axis (time)

using androidplot to set the number of values on the x-axis (see setDomainBoundaries)
rather than pass through the milliseconds for the times, we just use the index for the series (see  SimpleXYSeries.ArrayFormat.Y_VALS_ONLY) this allows us to then refer to our readingTimes list directly.