Switch commoncpp2 to ucommon to solve dependency conflicts.

libccrtp was depending on commoncpp2, and have been replaced by a version
depending on ucommon as well.
diff --git a/jni/libzrtp/sources/bnlib/ec/ecdh.h b/jni/libzrtp/sources/bnlib/ec/ecdh.h
index 7ec32ad..0cf083a 100644
--- a/jni/libzrtp/sources/bnlib/ec/ecdh.h
+++ b/jni/libzrtp/sources/bnlib/ec/ecdh.h
@@ -22,17 +22,15 @@
 /**
  * @brief Takes a secret large random number and computes the public EC point.
  *
- * @param curve is the curve to use.
+ * @param curve is the NIST curve to use.
  *
  * @param Q the functions writes the computed public point in this parameter.
  *
  * @param d is the secret random number.
  *
- * @return @c true (!0) if public key was computed, @c false otherwise.
- *
  * @sa ecGenerateRandomNumber
  */
-int ecdhGeneratePublic(const EcCurve *curve, EcPoint *Q, const BigNum *d);
+int ecdhGeneratePublic(const NistECpCurve *curve, EcPoint *Q, const BigNum *d);
 
 /**
  * @brief Computes the key agreement value.
@@ -40,7 +38,7 @@
  * Takes the public EC point of the other party and applies the EC DH algorithm
  * to compute the agreed value.
  *
- * @param curve is the curve to use, must be the same curve as used in
+ * @param curve is the NIST curve to use, must be the same curve as used in
  *              @c ecdhGeneratePublic.
  *
  * @param agreemtn the functions writes the computed agreed value in this parameter.
@@ -49,7 +47,7 @@
  *
  * @param d is the secret random number.
  */
-int ecdhComputeAgreement(const EcCurve *curve, BigNum *agreement, const EcPoint *Q, const BigNum *d);
+int ecdhComputeAgreement(const NistECpCurve *curve, BigNum *agreement, const EcPoint *Q, const BigNum *d);
 
 #ifdef __cplusplus
 }