upgrade-v1

[krlosMata]

Summary

Apply proper changes to hermez contract to support the following new features:

• new exits approach
• withdraw-multi-token
  • check specification here
• withdraw-bjj
  • check specification here

Overview changes

• remove variables regarding exit-tree
• update withdrawal approach to https://github.com/hermeznetwork/docs/blob/feature/update-v1/docs/developers/protocol/hermez-protocol/protocol.md#hermezwithdraw
• add withdraw-multi-token function

[laisolizq]

Spec WithdrawMultiToken: https://hackmd.io/6tABzjVKT4iX8W9_NhynOw

[jesusholoo]

Spec withdrawBjj https://hackmd.io/nFX5gHYsSUWyAsB5s3PQRg