gui: Update diagnostics

[jamescowens]

This is a PR to refresh the diagnostics and fix several bugs.

Currently this fixes the bug in the clock test when using ntp and also improves the clock test to not use the ntp call if enough
connections are present to use the GetTimeOffset().

Note that the code here will fail the clock test if the skew is 5 minutes or greater. I think this is reasonable as the disconnection and banning code in ProcessMessage() for nodes for time difference is

` int64_t timedrift = std::abs(GetAdjustedTime() - nTime);

    if (timedrift > (8*60))
    {
        LogPrint(BCLog::LogFlags::NOISY, "Disconnecting unauthorized peer with Network Time so far off by %" PRId64 " seconds!", timedrift);
        pfrom->Misbehaving(100);
        pfrom->fDisconnect = true;
        return false;
    }`

I have added a difficulty test. Closes #2071.

For documentation purposes, the difficulty test uses a "scale factor" of 1.0 for mainnet and 0.1 for testnet, and then the values of 1.0 and 5.0 for failure and warning for testnet and mainnet respectively. This means that mainnet will show a warning < 5.0 and a failure < 1.0. Testnet will show a warning < 0.5 and a failure < 0.1.

The tooltip is context sensitive. For the warning, it reads, "Your difficulty is very low and your wallet is probably forked. Please ensure you are running the latest version and try removing the blockchain database and resyncing from genesis using the menu option. (Note this will take 2-4 hours.)" For the failure, it reads, "Your difficulty is extremely low and your wallet is almost certainly forked. Please ensure you are running the latest version and try removing the blockchain database and resyncing from genesis using the menu option. (Note this will take 2-4 hours.)

Notice this anticipates the merge of #2093.

This also now includes context sensitive tooltips for all the tests to help people take actions to fix warnings and failures.

[jamescowens]

I actually think I may remove outboard connections and instead put a difficulty test in its place.

[cyrossignol]

I think a difficulty test could be useful. The outbound connection test may be worth keeping as a way to catch cases where peers ban a broken node that doesn't accept inbound connections.

[jamescowens]

I have put in context sensitive Tooltips which provide specific guidance for each test if in warning or failed status.

I will add back in the output connection test.

[jamescowens]

I did tooltips for the socket error enum. Let me know if you agree or disagree with the test status and conditional tooltips...

[jamescowens]

This is ready for review.

[div72]

ACK with a few nits.

[jamescowens]

Note with the latest commit, this is what the diagnostics look like on a healthy wallet syncing from zero...

[jamescowens]

Rebased to resolve conflict with #2093.