config: make refreshrate for mouse move/resize a config option

Bump the default from 60 to 120.

config.def.h

@@ -36,6 +36,7 @@ static const float mfact     = 0.55; /* factor of master area size [0.05..0.95]
 static const int nmaster     = 1;    /* number of clients in master area */
 static const int resizehints = 1;    /* 1 means respect size hints in tiled resizals */
 static const int lockfullscreen = 1; /* 1 will force focus on the fullscreen window */
+static const int refreshrate = 120;  /* refresh rate (per second) for client move/resize */
 
 static const Layout layouts[] = {
 	/* symbol     arrange function */