couch_log: use lager

With this change instead to use our own way to log file we are using
lager which improve the logging which will make couchdb more tolerant in
the face of large or many log messages, won't out of memory the node.

Note: Lager can handle multiple backend butwe are for now only handling
the file and console backend in the ini file. Other backends can be
configured using the app.config file.