Operation maintenance

[pepsi7959]

Log feature:

• All log will append to file
• Separate Application Log for tracking SIP message

Stat feature:

• count incoming and outgoing message
• count number of connections
• display essential status

Updated configuration:

  ...
  <log-path>/tmp/</log-path>
  <log-filename>webrtc2sip.log</log-filename>

  <app-log-level>INFO</app-log-level>
  <app-log-path>/tmp/</app-log-path>
  <app-log-filename>app.log</app-log-filename>

  <stat-path>/tmp/</stat-path>
  <stat-filename>webrtc2sip.stat</stat-filename>
  <stat-interval>5</stat-interval><!-- seconds -->
  <reset-enable>yes</reset-enable>
  ...

Required Dobango libs https://github.com/entronica/doubango/pull/5#issue-386539865