Add a new native contract to support ec curve operations and zk-SNARK verification

[kunxian-xia]

This new contract has six functions:

• ECAdd(): add two ec points on the alt_bn128 curve
• TwistECAdd(): add two ec points on the twist curve
• ECMul(): scalar multiplication on the alt_bn128 curve
• TwistECMul(): scalar multiplication on the twist curve
• PairingCheck(): check if e(a1, b1) ... e(ak, bk) == 1 where ai are points on the alt_bn128 curve and bi are points on the twist curve.
• PHGR13Verify(vk, proof, input): verify if a proof is a valid PHGR13 zk-SNARKs proof corresponding to the vk.

[Honglei-Cong]

fixes #810

[Honglei-Cong]

@kunxian-xia
Is there any project requiring this feature?
If not, suggest to commit to branch shard-common.
What you think? @kunxian-xia @laizy