Clean up function naming in RPC error module

[axelchalon]

I'm glad to have found somewhere to start :P

Closes #3204 ; here are the changes to the function names:

errors::encryption_error => errors::encryption
errors::encoding_error => errors::encoding
errors::database_error => errors::database
errors::from_fetch_error => errors::fetch
errors::from_signing_error => errors::signing
errors::from_password_error => errors::password
errors::from_transaction_error => errors::transaction
errors::from_call_error => errors::call

Let me know if you have better ideas for some names or if there are other things to be done!

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[axelchalon]

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[debris]

lgtm

[tomusdrw]

🎉