feat: use IPFS to store token goverance proposals

[troggy]

What does this PR do?

Adds:

• IPFS store to handle low-level work with IPFS
• create Proposal domain object to hold token governance proposal details
• create ProposalStore which is supposed to be used to get/save proposals (in pour case from IPFS). You may be interested to read how to use MobX's stores.
• changed tokenGovernance page to use Proposal object to store data and get hash from it.
• added some notification UI to tokenGovernance page to indicate IPFS uploading progress (it may take a while sometimes)
• registerProposal call moved into proposalStore

Recommendations for testing

Test UI for success/failure cases:

• user rejects tx
• user signs tx

check submitted proposal has correct hash

check that hash can be recovered back to ipfsHash?

Links to relevant issues or information

Closes #270

[troggy]

@cyan-one pushed an update — moved all the creation logic in a store as it should be