Feature/xdai

[hexyls]

closes #1409

PR does not include verification, we can add that later once the kleros/curate subgraph is up for xDai.

1. Add xDai as a new network to your wallet:
   Name: xDai
   RPC: https://rpc.xdaichain.com/
   Chain ID: 100
   Symbol: xDai
   Block explorer: https://blockscout.com/poa/xdai
2. Use https://bridge.xdaichain.com/ to convert dai on Ethereum to xDai
3. Send some xDai to the wrapped xDai address: 0xe91D153E0b41518A2Ce8Dd3D7944Fa863463a97d

[Mi-Lan]

Good job hexyls! Works flawlessly i tested these features:

• Market Creation
• Depositing liquidity
• Withdrawing liquidity
• Buy action
• Sell action
  Here is the market i created and tested it on http://localhost:3000/#/0x3fd8ead8df4f8700027a1e3c39dd74e3f430176e

[pimato]

replaced by #1262