Refactor user nonce logic.

[mariacarmina]

Fixes #648 .

Changes proposed in this PR:

• solve Invalid signature error
• fix bug in nonce endpoint
• convert & store provider nonces into integers.

[bogdanfazakas]

@mariacarmina i think there is a use case that is not well handled, if the address sent is a fresh one the provider returns a null response instead of creating a new entrance for the new address and return 0 maybe

[mariacarmina]

@mariacarmina i think there is a use case that is not well handled, if the address sent is a fresh one the provider returns a null response instead of creating a new entrance for the new address and return 0 maybe

I suggest to create a new entry and return the new nonce value instead of 0 or null.

[bogdanfazakas]

@mariacarmina i think there is a use case that is not well handled, if the address sent is a fresh one the provider returns a null response instead of creating a new entrance for the new address and return 0 maybe

I suggest to create a new entry an return the new nonce value instead of 0 or null.

yep agreed with the new nonce value, 0 was just a better alternative for null

[mariacarmina]

A fresh address will be stored as a new entry in a database with 1 as the nonce value.

[mariacarmina]

Tested on barge & mumbai a compute flow (end to end) and it worked as expected, without occurring InvalidSignatureError (I could start the C2D job, get the status & results of the algorithm, get the C2D envs successfully).
To mention that I tested these modifications on a separate VM (hosted in US) which has better hardware resources.

[alexcos20]

if we handle this in a new issue, then lgtm