Namespaces with a leading '_' character result in cloudant failures

When creating an action (or any other entity) in a namespace having a name that has a `_` as the leading character, the controller encounters the following error when saving the entity document in cloudant
```
[ERROR] [#tid_385] [CouchDbRestStore] [PUT] 'whisks' failed to put document: 'id: _xyz/abc, rev: null'; http status: '400 Bad Request' [marker:database_saveDocument_error:18:3]
```
As shown, the cloudant document id is based off of the entity's fully qualified name - which starts with the namespace name; in this example, the namespace is `_xyz`. According to https://console.bluemix.net/docs/services/Cloudant/api/document.html#documents cloudant document `_id` values may not have a leading `_` character, resulting in the cloudant request failure.

Possible solutions:
- Do not allow namespaces with leading `_` characters
- Escape any leading `_` character in the `_id` field