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/Octobot.cs

@@ -27,6 +27,9 @@ public sealed class Octobot
     public static readonly AllowedMentions NoMentions = new(
         Array.Empty<MentionType>(), Array.Empty<Snowflake>(), Array.Empty<Snowflake>());
 
+    public const string RepositoryUrl = "https://github.com/LabsDevelopment/Octobot";
+    public const string IssuesUrl = $"{RepositoryUrl}/issues";
+
     public static async Task Main(string[] args)
     {
         var host = CreateHostBuilder(args).UseConsoleLifetime().Build();