Improve netspeed widget icons

[janoamaral]

• [x] Use a reliable way to detect interface type (wifi, ethernet, etc)
• [x] Detect when network is down and show icon accordingly
• [x] Add a config flag to show local IP address (maybe public?)

This is the proposed design for down network

Icons:

• Wifi: f16c2
• Ethernet: f0319

Proposed design por IP address

Icon f0a5f