To provide paging/tailing abilty over logs

[enxebre]

At the moment when streaming the logs we have a pretty basic approach so we are tailing a fixed size of the file resulting in only 15 last minutes of logs being available to the user.

We should be able to provide paging and tailing ability for showing differents chunks of the log file under demand, i.e when scrolling up/down.

At the moment we are needing two request for streaming the last chunk of the log file:
/files/read.json?path=/master/log&offset=-1 -> gives the size of the file
/files/read.json?path=/master/log&offset=' + size-60000 + '&length=' + offset+100000 -> shows the last maximum lenght

This ticket should also reduce the number of request to one.

See:
https://github.com/apache/mesos/blob/master/src/webui/master/static/pailer.html
https://github.com/apache/mesos/blob/master/src/webui/master/static/js/jquery.pailer.js