Add_backend , list_providers Api-Version:2

IMPORTANT!!! Tests will fail! The purpose of this PR is to review the code. When we have reviewed the code, we'll update the test settings and run tests again.

NOTE1: This branch includes updated tests
NOTE2: This branch includes updated docs for GET /providers and POST /backends
NOTE3: Some weird css and js files are there for our docs (shpinx-build updated them)