Feature Page Improvements

Kernel Density Plot:
 - Every other series is disabled by default
 - X Axis can be log transformed or not

Dose Curve Statistics:
 - Z normalized stats plotted over dose curve
 - z- normalized cell number plotted too

Area Uner Curve Plot:
 - Area under the statistics curves calculated and plotted
 - Requires 'zoo' package

Adds is.even function to determine if a number is even

Minor tweaks to UI