client: saner configurable and disableable logging through CV9BLog object

Should produce nice-ish trimmed, newlined and indented logs like this
(instead of unruly dump() output) by default:

  Convergence.settings: Deserializing across transport: localhost : 8080
  Convergence.worker: Reading http headers...
  Convergence.proto: Reading from FD: PRFileDesc.ptr(ctypes.UInt64("0xac9ec240"))
  Convergence.worker: |
    Total headers: CONNECT fraggod.net:443 HTTP/1.1
    User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20130721 Firefox/24.0
    Proxy-Connection: keep-alive
    Connection: keep-alive
    Host: fraggod.net
  Convergence.pki: Calculating PKI root...
  Convergence.pki: Initializing certificate cache...

Currently can be disabled (per-component) and configured via CV9BLog object
parameters, which aren't exposed anywhere in the ui or about:config yet.
client: don't log loading of Logger.js