Legacy web support

[RangerMauve]

It'd be cool if this stuff worked on legacy browsers,

Here's what would need to be done:

• Add in dat-archive-web to get the DatArchive API
• Maybe get the xhr patcher and source rewriter from load-dat-page?
• Use //dfurl.hashbase.io instead of dat://dfurl.hashbase.io for resources

Hopefully I'm not missing anything, but I think that's all that'd need to be done.