Add BrowserConsoleHandler

BrowserConsoleHandler is an handler sending logs to browser's javascript console
with no browser extension required
Fix PHP 5.3 support for BrowserConsoleHandler
Some consmetic changes
Fix invalid output when message contain returns
Use more "unique" markers format for styling
Merge remote-tracking branch 'rs/browser-console-handler'
Refactor the browser console handler to keep more methods private, refs #303