feat: add `remoteheads` in head exchange

[gfanton]

closes #111

send remoteHeads aside localHeads

[codecov[bot]]

Codecov Report

Patch coverage: 33.33% and project coverage change: +0.08 :tada:

Comparison is base (326aee1) 62.88% compared to head (8dbca74) 62.97%.

:exclamation: Current head 8dbca74 differs from pull request most recent head 3bfc8df. Consider uploading reports for the commit 3bfc8df to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #125 +/- ## ========================================== + Coverage 62.88% 62.97% +0.08% ========================================== Files 37 37 Lines 2541 2544 +3 ========================================== + Hits 1598 1602 +4 - Misses 645 646 +1 + Partials 298 296 -2 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `62.97% <33.33%> (+0.08%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=berty#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/berty/go-orbit-db/pull/125?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=berty) | Coverage Δ | | |---|---|---| | [stores/basestore/base\_store.go](https://codecov.io/gh/berty/go-orbit-db/pull/125?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=berty#diff-c3RvcmVzL2Jhc2VzdG9yZS9iYXNlX3N0b3JlLmdv) | `59.00% <33.33%> (+0.37%)` | :arrow_up: | ... and [3 files with indirect coverage changes](https://codecov.io/gh/berty/go-orbit-db/pull/125/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=berty) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=berty). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=berty)

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[github-actions[bot]]

:tada: This PR is included in version 1.20.0 :tada:

The release is available on GitHub release

Your semantic-release bot :package::rocket: