Simplifi frontend app

The application is inherited from PancakeSwap application.

Added the ability to use two web3 connections simultaneously, download the lists of tokens for each chain, implemented interactions with dex contracts to:

1. add liquidity;
2. remove liquidity;
3. swap tokens from one chain to another.

Sequence diagrams

Add liquidity

Link to diagram presentation - http://is.gd/JYtC2v

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Swap

Link to diagram presentation - http://is.gd/63CbQ6

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Remove liquidity

Link to diagram presentation - http://is.gd/3srkHM