Companion support for Base32 CIDv1

[lidel]

This issue tracks changes required by our move to CIDv1 in Base32 (B32) as the new default.
Meta-issue is at: https://github.com/ipfs/ipfs/issues/337:

Lowercase identifiers are required in order to work with legacy URI, web browser security (sub)origins and the experimental Protocol Handler API. So we are moving to finish support for CIDv1 across the ecosystem, and use it as default (while still supporting CIDv0/Multihash).

Draft of TODOs

• Add experiment that defaults all CIDs in UI to cidv1b32
• Detect cidv1b32 in subdomains (Detect CID in subdomains #526)
• Make sure all issues with label:cidv1b32 are closed

Descoped:

• Detect CIDv0 (Base58) and provide option to convert it to cidv1b32
  • go-ipfs fixed lookup, no longer needed

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[lidel]

This is no longer needed with go-ipfs 0.5:

• native subdomain feature takes care of CID conversion (Migration to CIDv1 (default base32) specs#247 (comment))
• going forward, we want to leverage webui for sharing files, so code responsible for file import will be removed, no need to invest time in adding new features.