Created Xcode projects for all currently-built plugins.  Added Xcode workspace with "All" scheme for building GUI and all plugins.  Addressed some compiler warnings in plugin code.

Useful to estimate the noise levels on channels and to make a somewhat
objective decision on threshold.
Computation is very fast (running statistics). Right click clears up the
stats. Display is on the top left corner.
Currently only works for single channel electrodes (i.e., always
displays the 0th channel statistics).