Improve DHCP and IPv6 info

[yubiuser]

What does this PR aim to accomplish?:

Improves the shown IPv6 and DHCP info.

1. On smaller PADD sizes, the IPv6 checkbox showed the IPv6 Router advertisement status instead of the availability of an IPv6 address. I think this was misleading and the presence of IPv6 Router advertisement is less important than IPv6 'availability'
2. Always display if Pi-hole has the DHCP server turned on/off
3. If there was enough space, show the DHCP address range
4. If there was enough space, show one IPv6 address

Additionally

1. Fix the startup sequence when starting in 'mini'
2. Clear the screen once on startup to prevent remains from the startup sequence

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2. I have commented my proposed changes within the code and I have tested my changes.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)
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