AccountCallBuilder : add two methods for query filter

[challet]

Following stellar/go#1835 and according to https://www.stellar.org/developers/horizon/reference/endpoints/accounts.html, adds the ability to filter by

• account signer
• account trustee of an asset

[abuiles]

@challet thanks for tackling this! It looks good to me. Do you think it would make sense to add real data in the tests scenarios?

[challet]

@abuiles data responses added to the test cases.

Made me notice that several url formats are used along the tests, both in the axios mock fetches and in the HAL responses :

• https://horizon-testnet.stellar.org/
• https://horizon-live.stellar.org:1337/
• relative paths (/accounts, /ledgers)

Sometimes one not matching the other in the same test case.

[abuiles]

@challet

Made me notice that several url formats are used along the tests, both in the axios mock fetches and in the HAL responses

Good catch! Thanks for updating the tests to use the same path. I think it makes sense to settle on https://horizon-testnet.stellar.org in the examples - they might not be always valid since testnet resets, but that's fine.

[abuiles]

@challet Thanks! Btw, would you mind checking this for future commits https://github.com/pstadler/keybase-gpg-github - we try to have commits signed in our repos :)