Apply official naming guidelines to Octobot (#306)

1. The root namespace was changed from `Octobot` to
`TeamOctolings.Octobot`:
> DO prefix namespace names with a company name to prevent namespaces
from different companies from having the same name.
2. `Octobot.cs` was renamed to `Program.cs`:
> DO NOT use the same name for a namespace and a type in that namespace.
3. `IOption`, `Option` were renamed to `IGuildOption` and `GuildOption`
respectively:
> DO NOT introduce generic type names such as Element, Node, Log, and
Message.
4. `Utility` was moved out of the `Services` namespace. It didn't belong
there anyway
5. `Program` static fields were moved to `Utility`
6. Localisation files were moved back to the project source files. Looks
like this fixed `Message.Designer.cs` code generation

---------

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

TeamOctolings.Octobot/Responders/GuildUnloadedResponder.cs

@@ -0,0 +1,38 @@
+using JetBrains.Annotations;
+using Microsoft.Extensions.Logging;
+using Remora.Discord.API.Abstractions.Gateway.Events;
+using Remora.Discord.Gateway.Responders;
+using Remora.Results;
+using TeamOctolings.Octobot.Data;
+using TeamOctolings.Octobot.Services;
+
+namespace TeamOctolings.Octobot.Responders;
+
+/// <summary>
+///     Handles removing guild ID from <see cref="GuildData" /> if the guild becomes unavailable.
+/// </summary>
+[UsedImplicitly]
+public class GuildUnloadedResponder : IResponder<IGuildDelete>
+{
+    private readonly GuildDataService _guildData;
+    private readonly ILogger<GuildUnloadedResponder> _logger;
+
+    public GuildUnloadedResponder(
+        GuildDataService guildData, ILogger<GuildUnloadedResponder> logger)
+    {
+        _guildData = guildData;
+        _logger = logger;
+    }
+
+    public Task<Result> RespondAsync(IGuildDelete gatewayEvent, CancellationToken ct = default)
+    {
+        var guildId = gatewayEvent.ID;
+        var isDataRemoved = _guildData.UnloadGuildData(guildId);
+        if (isDataRemoved)
+        {
+            _logger.LogInformation("Unloaded guild {GuildId}", guildId);
+        }
+
+        return Task.FromResult(Result.Success);
+    }
+}