Ipv6 support

[Cobinja]

This adds IPv6 support.

There are several cases:
a) both devices can do both IP versions: IPv4 is used for compatibility
b) one device can only do IPv6: IPv6 is used
c) one device can only use IPv4 and the other can only use IPv6: there's nothing to do, since those devices can't communicate with each other.

@slowscript :
The QR code changes a bit:

On devices with support for IPv4 (example: 192.168.1.10) and IPv6 (example: 2a02::1), the code will look like this:
warpinator://192.168.1.10:42001/ipv6=2a02%3A%3A1 (%3A is ':')

On devices that only use IPv6 but not IPv4, the IPv6 address will be used for the host part in the QR code url:
warpinator://[2a02::1]:42001 (brackets indicate IPv6)

On devices that only use IPv4, the QR code doesn't change.

[Cobinja]

@slowscript
Sorry, I made a slight mistake in my first comment above.
The QR code data on devices that support both IP versions is:
warpinator://192.168.1.10:42001?ipv6=2a02%3A%3A1 (%3A is ':')
Note the question mark instead of a slash before 'ipv6='

[slowscript]

So I finally found some time to test the manual connection part. Devices that only use IPv6 are not a concern, as they never worked. On devices that use both versions, the Android port works fine (it parses the URL with a built-in method that has full URL support) and just connects on IPv4. The Windows version however does not, it parses the IP string using a regex that only applies to IPv4 addresses and fails with an invalid address error. I will need to fix this in an update, I don't think there is a way to add the functionality and not break it, my mistake. Typing the address manually works as usual. Most Windows and Linux users probably won't be scanning the QR code anyway.

I would suggest to not show the user this very long string (user might think that it is necessary to type all of it)

and instead put the two addresses each on a separate line, so the user can choose which to use, e.g.:

192.168.0.10:42001
[2001:abc:def::10]:42001

[Cobinja]

That's a good idea. Done.