gsr: Added gsr sensor C source

Added the C source for the gsr sensor with necessary changes to cmake,
examples, docs.

    * Renamed all files with grovegsr to gsr
    * Replaced all instances of grovegsr with gsr
    * Added C source for gsr sensor
    * Updated all cmake files
    * Added C example for gsr sensor
    * Fixed C++ threshold method from throwing on a successfull aio read

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/grovegsr/javaupm_grovegsr.i

@@ -1,19 +0,0 @@
-%module javaupm_grovegsr
-%include "../upm.i"
-
-%{
-    #include "grovegsr.hpp"
-%}
-
-%include "grovegsr.hpp"
-
-%pragma(java) jniclasscode=%{
-    static {
-        try {
-            System.loadLibrary("javaupm_grovegsr");
-        } catch (UnsatisfiedLinkError e) {
-            System.err.println("Native code library failed to load. \n" + e);
-            System.exit(1);
-        }
-    }
-%}