Move remaining Horizon calls to backend

[aristidesstaffieri]

We aim to move all data fetching to our backend in order to move away from Horizon and setup for a multi platform future.
We should find ways to moving the following remaining Horizon calls to the backend -
server.loadAccount(..pubkey..)
server.accounts()
server.feeStats()
server.assets()
server.checkMemoRequired()

Should we move these?
Federation.Server.resolve()