[Server] Add ability to create static attributes.

This allows creating instances of services/characteristics and decriptors without
needing to call the parent createX() methods. This allows creation of the attibutes
within a class or other structure and the attributes can be linked to the parent by
calling the parent addX() method.

Additonally this increases the backward compatibility with the original bluedroid library
to further support user migration.

src/NimBLE2904.h

@@ -42,6 +42,7 @@ struct BLE2904_Data {
  */
 class NimBLE2904: public NimBLEDescriptor {
 public:
+    NimBLE2904(NimBLECharacteristic* pCharacterisitic = nullptr);
     static const uint8_t FORMAT_BOOLEAN   = 1;
     static const uint8_t FORMAT_UINT2     = 2;
     static const uint8_t FORMAT_UINT4     = 3;
@@ -77,7 +78,6 @@ public:
     void setUnit(uint16_t unit);
 
 private:
-    NimBLE2904(NimBLECharacteristic* pCharacterisitic);
     friend class NimBLECharacteristic;
     BLE2904_Data m_data;
 }; // BLE2904