Improve URL validation to check for a valid host.

Parsing a URL with `URI` is not sufficient as the following cases
are considered valid:

URI.parse("http://https://google.com")
=> #<URI::HTTP http://https//google.com>

spec/components/validators/url_validator_spec.rb

@@ -0,0 +1,33 @@
+require 'rails_helper'
+require 'validators/topic_title_length_validator'
+
+RSpec.describe UrlValidator do
+  let(:record) { Fabricate.build(:user_profile, user: Fabricate.build(:user)) }
+  let(:validator) { described_class.new(attributes: :website) }
+  subject(:validate) { validator.validate_each(record, :website, record.website) }
+
+  [
+    "http://https://google.com",
+    "http://google/",
+    "ftp://ftp.google.com",
+    "http:///what.is.this",
+    'http://meta.discourse.org TEST'
+  ].each do |invalid_url|
+    it "#{invalid_url} should not be valid" do
+      record.website = invalid_url
+      validate
+      expect(record.errors[:website]).to be_present
+    end
+  end
+
+  [
+    "http://discourse.productions",
+    "https://google.com",
+  ].each do |valid_url|
+    it "#{valid_url} should be valid" do
+      record.website = valid_url
+      validate
+      expect(record.errors[:website]).to_not be_present
+    end
+  end
+end