feat(locksmith) Single web3service locksmith

[julien51]

Description

I was investigating some issues yesterday and realized we were wasting a lot of RPC requests because we instantiate a new web3 service every time.
With this change we should now be re-using an instance.

Checklist:

• 1 PR, 1 purpose: my Pull Request applies to a single purpose
• I have commented my code, particularly in hard-to-understand areas
• I have updated the docs to reflect my changes if applicable
• I have added tests (and stories for frontend components) that prove my fix is effective or that my feature works
• I have performed a self-review of my own code
• If my code involves visual changes, I am adding applicable screenshots to this thread

Release Note Draft Snippet

[julien51]

We should probably do something similar in unlock-app in fact. The reason is that unlock-js has a caching mechanism that means we don't need to do as many RPC requests.