manager: led priority is optional

The default priority was "Blink" but now the priority is optional.

This helps to implement group priority.
So if someone wants to use group priority they can do so, without the
default led priority getting in the way.

The led priority can still be assigned as "Blink" explicitly if needed.

Change-Id: I9336487bcc2edc0b3308ee76eb5330b8222b7f25
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/manager/ledlayout.hpp b/manager/ledlayout.hpp
index c11500f..a609df6 100644
--- a/manager/ledlayout.hpp
+++ b/manager/ledlayout.hpp
@@ -27,7 +27,7 @@
     Action action;
     uint8_t dutyOn;
     uint16_t period;
-    Action priority;
+    std::optional<Action> priority;
 
     // Order LEDs such that same LEDs are grouped next to
     // each other and the same LEDs are in priority order