use menu helper for quadcopter pages

input/blog/2015/2015_12_20_serialgamepad.md

 flattr: true
 github: https://github.com/xythobuz/SerialGamepad
 parent: projects
+show_in_quadcopters: true
 position: 50
 ---
 

input/blog/2016/2016_07_24_usb_host_cppm.md

 flattr: true
 github: https://github.com/xythobuz/Saitek-X52-PPM
 parent: projects
+show_in_quadcopters: true
 position: 80
 ---
 

input/blog/2016/2016_11_05_frsky_telemetry.md

 flattr: true
 github: https://github.com/xythobuz/FrSky-Telemetry-Arduino
 parent: projects
+show_in_quadcopters: true
 position: 90
 ---
 

input/projects/quadcopters.md

 <!--%
 printQuadcopterMenu()
 %-->
+
+The following projects are also related to my Quadcopter endeavours.
+
+<!--%
+printQuadcopterRelatedMenu()
+%-->

macros.py

     for p in mpages:
         printMenuItem(p, False, True, True)
 
+def printQuadcopterRelatedMenu():
+    mpages = [p for p in pages if p.get("show_in_quadcopters", "false") == "true"]
+    mpages.sort(key=lambda p: [p.get("date", "9999-01-01")], reverse = True)
+    for p in mpages:
+        printMenuItem(p, False, True, True)
+
 def printRobotMenuEnglish():
     mpages = [p for p in pages if p.get("parent", "") == "xyrobot" and p.lang == "en"]
     mpages.sort(key=lambda p: int(p["position"]))