Add raw HF signal plotting (#786)

* Add raw HF signal plotting
* new fpga module hi_get_trace.v - store A/D converter output to circular buffer on FPGA
* new command 'hf plot' - pull data from FPGA and display it in Graph Window

include/usb_cmd.h

@@ -220,6 +220,7 @@ typedef struct{
 #define CMD_MIFARE_DESFIRE                                                0x072e
 
 #define CMD_HF_SNIFFER                                                    0x0800
+#define CMD_HF_PLOT                                                       0x0801
 
 #define CMD_UNKNOWN                                                       0xFFFF