Formats mapping and removes first two levels

I wasn't able to load the mapping unless I removed the first two levels (`congress` and `mappings`) -- it looks like those were attempting to update all mappings in the `congress` index at once.

This mapping begins at the collection-level:

```json
{
  "congressional_documents": {
    "properties": {
      "bill_id": {
        "type": "string"
      },
  ...
}
```

And is in line with the other mappings in `config/mappings/`.

I also ran the JSON through a JSON formatter to normalize the tabs to be more readable, and to match the other mappings.

This can now be loaded using the rake task. The first run with `force=1` notes that the index already exists, and then notes (for me, locally) that the mapping didn't need to be deleted because it doesn't exist, and then correctly indexes the mapping.

```
$ rake elasticsearch:init force=1 only=congressional_documents

running: curl -XPUT 'http://127.0.0.1:9200/congress'
{"error":"IndexAlreadyExistsException[[congress] already exists]","status":400}
Ensured index exists

running: curl -XDELETE 'http://127.0.0.1:9200/congress/_mapping/congressional_documents/'
{"error":"TypeMissingException[[_all] type[[congressional_documents]] missing: No index has the type.]","status":404}
Deleted congressional_documents

running: curl -XPUT 'http://127.0.0.1:9200/congress/_mapping/congressional_documents' -d @config/mappings/congressional_documents.json
{"acknowledged":true}
Created congressional_documents
```

If re-running with the same parameters, it correctly drops and re-loads the mapping (which drops all data in the collection):

```
$ rake elasticsearch:init force=1 only=congressional_documents

running: curl -XPUT 'http://127.0.0.1:9200/congress'
{"error":"IndexAlreadyExistsException[[congress] already exists]","status":400}
Ensured index exists

running: curl -XDELETE 'http://127.0.0.1:9200/congress/_mapping/congressional_documents/'
{"acknowledged":true}
Deleted congressional_documents

running: curl -XPUT 'http://127.0.0.1:9200/congress/_mapping/congressional_documents' -d @config/mappings/congressional_documents.json
{"acknowledged":true}
Created congressional_documents
```

The mapping can be verified by visiting `http://localhost:9200/congress/congressional_documents/_mapping` in your browser.