improve (Wasabi is) offline detection

[MarnixCroes]

General Description

Wasabi should detect faster that it is offline and display this to the user. Instead of keep displaying that it is online.

I'm not familiar with this, nor did I look at the code, but it could definitely use some improvement.

The status icon should have some feedback that it is offline. i.e. indexer not connected (anymore)

How To Reproduce?

1. launch Wasabi
2. everything connects
3. turn off internet
4. Wasabi will keep displaying it is online (I only tried till 15 min, not sure if/what is the max)

Wasabi Version

4ba60a19ccbe6dfe40a3799be3a5a5d5eba96586