Implemented the deletion function

Closes #17

I18N Commander/Processor/SectionProcessor.cs

@@ -82,4 +82,30 @@ public static class SectionProcessor
         await db.SaveChangesAsync();
         return section;
     }
+
+    public static async Task RemoveSection(DataContext db, string selectedKey)
+    {
+        // Remove the section from the database:
+        var section2Delete = await db.Sections.FirstOrDefaultAsync(n => n.DataKey == selectedKey);
+        if (section2Delete is null)
+            throw new ArgumentException($"The section with key {selectedKey} does not exist in the database.");
+        
+        // Next, remove all children of the section, and the children's children, etc.:
+        var children = await db.Sections.Where(n => n.Parent == section2Delete).ToListAsync();
+        foreach (var child in children)
+            await RemoveSection(db, child.DataKey);
+
+        db.Sections.Remove(section2Delete);
+        await db.SaveChangesAsync();
+    }
+    
+    public static async Task<int> NumberChildren(DataContext db, string selectedKey)
+    {
+        // Read the section from the database:
+        var section = await db.Sections.FirstOrDefaultAsync(n => n.DataKey == selectedKey);
+        if (section is null)
+            throw new ArgumentException($"The section with key {selectedKey} does not exist in the database.");
+        
+        return await db.Sections.CountAsync(n => n.Parent == section);
+    }
 }