Index past referenda

[stephanie-olp]

Currently, we only have the ongoing referenda displayed in the app
We would like to add the past ones (both the one who passed and the one who didn't)

[stephanie-olp]

Data that need to be indexed :

• Proposal ID
• Title of the proposal (if there is one)
• Proposal Description (if there is one)
• Type of action (module)
• Proposal hash
• Proposal author
• Date the proposal became a referendum
• Date of the last update
• Status
• Results of the referendum (number of aye & nye + failing threshold)
• List of people who voted on the referendum : accounts name + locked value + vote (aye or nye)
• Link to polkassembly discussion

[stephanie-olp]