add more nimble example

1. make heart rate sensor example really work
using nRF Toolbox HRM
2. add master device scan example
3. add gatt server example(seems not working)

examples/nimble_heart_rate_sensor/README_en.md

@@ -0,0 +1,13 @@
+NimBLE Heart Rate Sensor Example
+================================
+This example demonstrates how to implement asynchronous data transfer using GATT
+notifications by implementing a mock-up BLE heart rate sensor. Once flashed on
+a node, you can connect to it using any phone or device capable of using such a
+heart rate sensor, e.g. Nordics `nRF Toolbox` for Android
+(https://play.google.com/store/apps/details?id=no.nordicsemi.android.nrftoolbox).
+
+The heart rate sensor is simulated by simply providing an up- and down counter
+for its BPM value.
+
+On top of the heart rate service, this example implements the device information
+as well as the battery service.