WebUI Integration

Dear fellows of @ipfs-shipyard/gui!

I was taking a look at how to integrate this with WebUI. The initial idea was to provide a link to `share.ipfs.io/add/QmHash1/QmHash2` with the hashes of the files to add.

Issues I found and other problems worth mentioning:

- It only supports ony hash on `/add` url.
- It breaks when going to `share.ipfs.io/add` without any hash.
- `share.ipfs.io` won't be able to connect via API if the user doesn't explicitly allow that URL
- If using `window.ipfs` it can be slower because it will use public API instead of user's node.
- We can't grant that when moving from WebUI ---> Share APP will use the same IPFS instance since WebUI allows us to change the instance it is connected to.

I'll work on the first issues. The other ones need more thought. Thoughts?

Start by tracing the `/add` URL entry point and the WebUI integration described in issue #25. Verify how multiple hashes are parsed and how the no-hash case is handled, then confirm both behaviors from the resulting WebUI flow; the API and shared-IPFS-instance concerns are explicitly left for further thought.

Written by the indexing model from the issue text.