Feat/extract http client from alfresco api client

[mserwicki]

Please check if the PR fulfills these requirements

[x] The commit message follows our [guidelines](https://github.com/Alfresco/alfresco-js-api/wiki/Commit-format)
[x] Tests for the changes have been added (for bug fixes / features)
[ ] Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x")

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] Documentation
[ ] Other... Please describe:

What is the current behavior? (You can also link to an open issue here)

Currently we are not able to provide custom implementation for http client, and all calls are made with superagent

What is the new behavior?

We are able to create AlfrescoApi instance with custom http client.

Does this PR introduce a breaking change? (check one with "x")

[ ] Yes
[x] No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

[popovicsandras]

All seems good, but I guess this file needs some alignment as well:
api-codegen/src/main/resources/api-code-gen/base.api.mustache

[popovicsandras]

But please do not merge it yet, only after the release