Local find bar for sites that don't handle ctrl+f

[sardination]

Feature Description
We want the find bar to behave like it does on a fully local browser. This means that ctrl+f should open a local browser find bar unless the page itself intercepts a ctrl+f and has its own find bar (like Google Docs).

The Problem It Fixes
Currently, the <whist> tag unconditionally grabs ctrl+f and so the find bar that is shown is in the streamed window from the server.

Potential Implementation(s)
We would need to roughly follow these steps:

1. Grab the find contents of the find bar
2. Send find contents over to server
3. Do the search on the server without showing the find bar

We would also have to allow pages that already intercept the find bar (like Google Docs) to continue to do that.

[philippemnoel]