gui(intsaller): ping electrum backend both with tcp & ssl

[pythcoiner]

This PR add a double ping (both tcp & ssl) when defining an electrum server address.
After ping if the prefix is not ssl we display a warning to the user:

[nondiremanuel]

I won't comment on the technical solution, but on the UI side I would use yellow/orange (the usual warning color) for warnings. I would possibly make it a little bigger

[pythcoiner]

• the size is the usual size we use for warning/error on not valid field, so i think we should keep this one
• will change the color

[pythcoiner]

[jp1ac4]

Do we need to warn about SSL if people are using on their local network?

[jp1ac4]

Wouldn't it be simpler to have a "Use SSL" checkbox?

[pythcoiner]

the advantage of ping both is i guess almost the time our user will not know what is ssl, so w/ this solution they don't have to care about.

[pythcoiner]

Do we need to warn about SSL if people are using on their local network?

i think it's not easy to be sure wether we are a local network or not