Memory utilization widget changes

Add download icon on title bar, and remove button
Add event and empty event handler to base widget class
Merge pull request #150 from sujeetsr/issue#112_mem_util_changes

Memory utilization widget changes
Memory utilization

Use alt download icon on title bar
Merge pull request #151 from sujeetsr/issue#112_mem_util_changes

Memory utilization
Add preliminary API support for network interfaces.

Add API support to scan network interfaces and configure them. Implement low
level network configuration code to use in the API implementation via a
separate Network view. Add network interface model, serializer and generate the
db migration file. Add CLI support for basic network device scan.
Add network utilization smart probe API support.

Create network utilization model in smart manager, serializer and db migration
file. Implement data collection in ProcRetreiver. Add url layout similar to
other smart probes(/sm/sprobes/netstat) and create the API view.
Merge branch 'issue#111_network_util' of https://github.com/schakrava/rockstor-core into issue#111_network_util
Add helper code to process raw network utilization data.
Merge branch 'issue#111_network_util' of https://github.com/schakrava/rockstor-core into issue#111_network_util
Network utilization

Add networkinterface model
Add network interface configuration to setup
Network utilization

Add network utilization widget
Add flot axislabel plugin for axis labels
Change modal position to absolute in style.css so that bootstrap modals
can be scrolled
Network utilization

Add code to display values for data and packets
Network setup

Change text for protocol
Update network utilization model to include interface name.
Fix bugs in network utilization code. Ignore quotes and extra characters while
retrieving device configuration. Update the view to verify object existence
properly.
Network utilization

Get interfaces
Add interface select dropdown
Display selected interface data
Return empty config for network devices present but without any prior
configuration.