Improve documentation and remove internal references

[jaymindesai]

Acceptance Criteria

• Use Java code blocks in the markdown instead of generic single-tab blocks

import com.ibm.cusp.graph.stages.Stages;

public interface WidgetStages extends Stages {
    String RECEIVE_REQUEST = "receiveRequest";
    String PARSE_REQUEST = "parseRequest";
    String PLACE_ORDER = "placeOrder";
    String SEND_EMAIL = "sendEmail";
    String LOG_REQUEST = "logRequest";
    String QUERY_INVENTORY = "queryInventory";
    String QUERY_BACKUP_SYSTEM = "queryBackupSystem";
    String MANUFACTURE_WIDGETS = "manufactureWidgets";
}

• Fix typos in the README
• Remove internal references (example: it_recovers_from_failed_reranked_search_and_qpp_when_basic_search_succeeds) from the unit tests. Update the method and variable names in unit tests to be in sync with the widget stages from the README.