WIP: Hook cache up to the charmbrowser and charm details views 

I looked into this further.

`entityId` (the id parsed out of the url into the metadata) for a bundle and charm are in the format: `bundle/mongodb/5/cluster` and `precise/mysql-45` respectively. 

In the bundle the available id's are in the format:
```
id: "~charmers/mediawiki/6/single"
branch_spec: "~charmers/charms/bundles/mediawiki/bundle"
bundleURL: "bundle:mediawiki/6/single"
permanent_url: "bundle:~charmers/mediawiki/6/single"
```

And in the charm:
```
charm_path: "charms/precise/mysql-45/json"
full_name: "precise/mysql"
id: "cs:precise/mysql-45"
storeId: "precise/mysql-45"
url: "cs:precise/mysql-45"
```

So because of the complexity of the urls the best approach is still the one that I implemented with the prefix adding and then the parsing of that path in the `getEntity` method in the cache.