Fix bug in RT130 when the selected time has no data

• Check SOH epoch time before adding data point to a channel
• Calculate total data points in a data set so it can report when the selected time doesn't contain data
• Request user to clear TPS/RAW checkboxes if some of them are checked but no waveform channel is selected.
• Fix bug when plotting empty channel so that empty channel can still be plotted with total of data point labeled '0'.

closes #208 (closed)