- Database namespace is now NadekoBot.Db

- Db related code is now in src/NadekoBot/Db
- Finished major part of the db refactor, but many optimizations are left to be made

src/NadekoBot/Db/Extensions/SelfAssignableRolesExtensions.cs

@@ -0,0 +1,26 @@
+using NadekoBot.Core.Services.Database.Models;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.EntityFrameworkCore;
+
+namespace NadekoBot.Db
+{
+    public static class SelfAssignableRolesExtensions
+    {
+        public static bool DeleteByGuildAndRoleId(this DbSet<SelfAssignedRole> roles, ulong guildId, ulong roleId)
+        {
+            var role = roles.FirstOrDefault(s => s.GuildId == guildId && s.RoleId == roleId);
+
+            if (role == null)
+                return false;
+
+            roles.Remove(role);
+            return true;
+        }
+
+        public static IEnumerable<SelfAssignedRole> GetFromGuild(this DbSet<SelfAssignedRole> roles, ulong guildId) 
+            =>  roles.AsQueryable()
+                    .Where(s => s.GuildId == guildId)
+                    .ToArray();
+    }
+}