complete search rewrite

[rlidwka]

Current search code is based on the PR #65, which was using a primitive approach:

• get /-/all from npmjs
• use JSON.parse() on it, trying to parse it's entire output into memory
• print the entire json body to the client afterwards

Now that npm database it larger, the 3rd step is usually getting replaced with "eat up 2+GB of memory and crash" step.

So I changed it to use streaming, and now it works like this:

• get /-/all from npmjs
• use JSONStream and parse each package in the output
• for each package, check permissions and write it to the client, proceed to the next one

This should fix most of our search-related issues. By the way, on my computer npm is still crashing trying to parse the entire all.json, so whoever has a time and patience for it, please check if this commit works. :)