Add issue button w/ some button updates (#221)

In this PR, I've added a "Report an issue" button and a few more
button-related changes:
- Add "Report an issue" button
- Add icon for "Octobot's source code"
- Rename `AboutTitleRepository` to `ButtonOpenRepository`
- Rename `OpenEventInfoButton` to `ButtonOpenEventInfo` to be consistent
with other language string names
- Rename `ColorsList.cs` to `Miscellaneous.cs`
- Add public const strings in `Octobot.cs` to get repository & issues links

---------

Signed-off-by: mctaylors <cantsendmails@mctaylors.ru>

src/Services/Update/ScheduledEventUpdateService.cs

@@ -222,7 +222,7 @@ public sealed class ScheduledEventUpdateService : BackgroundService
 
         var button = new ButtonComponent(
             ButtonComponentStyle.Link,
-            Messages.OpenEventInfoButton,
+            Messages.ButtonOpenEventInfo,
             new PartialEmoji(Name: "📋"),
             URL: $"https://discord.com/events/{scheduledEvent.GuildID}/{scheduledEvent.ID}"
         );