Add isReadyToFly function

Provide isReadyToFly boolean instead of waiting for takeoff to finish.
It is now up to the user to check if the drone is ready to receive commands.

mavsdk_wrapper.cpp

@@ -290,6 +290,7 @@ int start(const char * ip, int port, const char * log_file, int timeout) {
     telemetry->subscribe_landed_state([](const Telemetry::LandedState landed_state) {
         if (landed_state == Telemetry::LandedState::InAir) {
             is_in_air = true;
+            doAction(&Action::transition_to_fixedwing, "Transition to fixedwing failed");
         }
     });
 
@@ -345,23 +346,7 @@ int arm(void) {
 
 int takeOff(void) {
     action->set_takeoff_altitude(DEFAULT_OVERRIDE_ALTITUDE);
-    if (doAction(&Action::takeoff, "Takeoff failed"))
-        return -1;
-
-    return 0;
-}
-
-int takeOffAndWait(void) {
-    if (takeOff() < 0)
-        return -1;
-
-    while (telemetry->flight_mode() != Telemetry::FlightMode::Takeoff)
-        sleep_for(seconds(1));
-    while (telemetry->flight_mode() == Telemetry::FlightMode::Takeoff)
-        sleep_for(seconds(1));
-
-    return doAction(&Action::transition_to_fixedwing,
-                    "Transition to fixedwing failed");
+    return doAction(&Action::takeoff, "Takeoff failed");
 }
 
 int triggerParachute(void) {
@@ -471,6 +456,10 @@ int healthAllOk(void) {
     return telemetry->health_all_ok();
 }
 
+int isReadyToFly(void) {
+    return is_in_air;
+}
+
 int isLanding(void) {
     if (is_in_air && telemetry->landed_state() != Telemetry::LandedState::InAir)
         return 1;