Logserver improvements:

* Check and enforce log threshold according to each app's loglevel's usage instead of according to each app's usage. In the earlier implementation if there were many INFO logs then it could end up deleting important FATAL / ERROR logs.

* Create a new section in the output that allows you to jump to an app's logs. Staged here: http://piraeus.cnc.corp.google.com:10115/

* Output the size of each log file and added a download link next to the size. Staged here: http://piraeus.cnc.corp.google.com:10115/

* Fixed bug where the number of log files was sent to InfluxDB instead of the number of lines inside each log file.

BUG=skia:3132

Review URL: https://codereview.chromium.org/728703003