github: Summer cleaning

[Morriar]

Some cleaning to the github lib.

Most interesting changes:

• kill github_curl and migrate clients (github_merge, github_search_for_jni)
• clean deserialization process heuristics for something more robust and readable (but a bit slower)
• array pagination
• kill GithubEntity
• remove ISO date methods
• mock testing for github::wallet
• wallet uses a Logger

This PR can be read commit by commit.

[Morriar]

I did read it ! 🏅

Congratz! :trophy: