Support meta-txs

[facuspagnuolo]

Idea

User story

As as user, I want to be able to interact with an Aragon application without being require to have funds in my wallet.

Technical requirements

To let the user seamlessly interact with Aragon without needing ETH, we need to implement meta-transaction support in aragonOS, implement at least 1 relayer, and the necessary changes to the signer panel.

Implementation

• Assess ecosystem status regarding meta-txs - link (sprint 14)
• MVP implementation of aragonOS contracts - PR 526 (sprint 14)
• Review and discuss scope with Jorge (sprint 14)
• Off-chain service implementation - PR 527 (sprint 14)
• Review full implementation (sprint 15)