Simplified paramLib access and show error messages for one poll cycle

Simplified getting and setting paramLib entries via a macro and created
a mechanism within poll() which makes sure that error messages are shown
for at least one poll cycle. Also moved MAXBUF_ to the SinqController
level.

src/sinqController.cpp

@@ -495,7 +495,7 @@ asynStatus sinqController::checkComTimeoutWatchdog(sinqAxis *axis) {
     asynStatus status =
         checkComTimeoutWatchdog(axis->axisNo(), errorMessage, MAXBUF_);
     if (status == asynError) {
-        setAxisParamChecked(axis, motorMessageText, motorMessage);
+        setAxisParamChecked(axis, motorMessageText, errorMessage);
     }
     return status;
 }