Make getHTTPRequest() at least somewhat sane
Make getHTTPRequest() at least somewhat sane

This code really needs replacement with a proper HTTP library but for now at
least fix the most glaring issues, including:

- Add a TODO to get this removed
- Don't busy wait with recv(…, MSG_DONTWAIT) for no gain over blocking and 100%
  CPU use
- Actually extract the headers instead of leaving them empty
- Just use a string instead of a std::ostringstream and converting back and forth
- Don't use NULL terminated string APIs when we have nice ones
- Add some useful comments on what the ifs actually test

Buchhold/QLever,Buchhold/QLever,Buchhold/QLever,Buchhold/QLever,Buchhold/QLever