Add tables and columns properties to RPC joinable_tables API

[seancolsen]

In the REST API, the joinable_tables API returned an object like this:

{
  "joinable_tables": [
    // ...
  ],
  "tables": [
    // ...
  ],
  "columns": [
    // ...
  ],
}

The corresponding RPC API only returns an array of joinable table objects.

The front end needs the tables and columns properties too. Can we please add those back?

[Anish9901]

@seancolsen
Instead of having tables and columns separate are you okay if its combined?

Before

{
  "tables": {
    "10": {
      "name": "Authors",
      "columns": [1, 2, 26]
    }
  },
  "columns": {
    "1" : {"name": "First Name", "type": "text"   },
    "2" : {"name": "Last Name" , "type": "text"   },
    "26": {"name": "id"        , "type": "integer"}
  }
}

After

"tables": {
  "10": {
    "name": "Authors",
    "columns": {
        "1" : {"name": "First Name", "type": "text"   },
        "2" : {"name": "Last Name" , "type": "text"   },
        "26": {"name": "id"        , "type": "integer"}
     }
  }
}

[seancolsen]

are you okay if its combined?

I replied in the PR.