Add get-predeployed-accounts function

[qperrot]

Usage related changes

• Implementation of get-predeployed-accounts function, which return an array of objects, containing the data of all pre-deployed accounts (which are: address, initial_balance, private and public keys).
  • A clientside function for accessing the /predeployed_accounts endpoint on Devnet.

Development related changes

• Upgrade to devnet v0.2.5
• Update TOKEN_ADDRESS used in test
• Fix formatting

Checklist:

• I have formatted the code
• I have performed a self-review of the code
• I have rebased to the base branch
• I have documented the changes
• I have updated the tests
• I have created a PR to the plugin branch of starknet-hardhat-example.

[FabijanC]

This PR is blocked by this one: 0xSpaceShard/starknet-devnet#138
After that PR is merged, a new devnet version should be released (and plugin configured to use it in its tests).