First-cut of a refactored failsafe system.

* fixes issue where indicators would flash when SBus RX entered failsafe
mode.
* fixes bug where turning off a TX for an SBus RX would instantly disarm
when using a switch to arm when the channel went outside the arming
range.
* introduces failsafe phases to make the system more understandable.
* allows the system to ask if rxSignalIsBeing received for all RX
systems: PPM/PWM/SerialRX/MSP.  Also works when a serial data signal is
still being received but the data stream indicates a failsafe condition
- e.g.  SBus failsafe flags.
* failsafe settings are no-longer per-profile.

Untested: Sumd/Sumh/XBus/MSP (!)
Tested: SBus X8R, Lemon RX Sat, X8R in PWM, Spektrum PPM.

src/main/io/display.c

@@ -51,6 +51,7 @@
 
 #include "flight/pid.h"
 #include "flight/imu.h"
+#include "flight/failsafe.h"
 
 #ifdef GPS
 #include "io/gps.h"
@@ -203,6 +204,33 @@ void updateTicker(void)
     tickerIndex = tickerIndex % TICKER_CHARACTER_COUNT;
 }
 
+void updateRxStatus(void)
+{
+    i2c_OLED_set_xy(SCREEN_CHARACTER_COLUMN_COUNT - 2, 0);
+    i2c_OLED_send_char(rxIsReceivingSignal() ? 'R' : '!');
+}
+
+void updateFailsafeStatus(void)
+{
+    char failsafeIndicator;
+    switch (failsafePhase()) {
+        case FAILSAFE_IDLE:
+            failsafeIndicator = '-';
+            break;
+        case FAILSAFE_RX_LOSS_DETECTED:
+            failsafeIndicator = 'R';
+            break;
+        case FAILSAFE_LANDING:
+            failsafeIndicator = 'l';
+            break;
+        case FAILSAFE_LANDED:
+            failsafeIndicator = 'L';
+            break;
+    }
+    i2c_OLED_set_xy(SCREEN_CHARACTER_COLUMN_COUNT - 3, 0);
+    i2c_OLED_send_char(failsafeIndicator);
+}
+
 void showTitle()
 {
     i2c_OLED_set_line(0);
@@ -573,8 +601,11 @@ void updateDisplay(void)
 #endif
     }
     if (!armedState) {
+        updateFailsafeStatus();
+        updateRxStatus();
         updateTicker();
     }
+
 }
 
 void displaySetPage(pageId_e pageId)