Disable import of theme config by default

Users can *opt-in* by setting `import_theme_config: true` in their config
file.

features/theme_configuration.feature

@@ -3,24 +3,16 @@ Feature: Bundling Config file with Theme gems
   I want to be able to pre-configure my gemified theme
   In order to make it easier for other Jekyllites to use my theme
 
-  Scenario: Easy onboarding with a pre-configured theme
-    Given I have a configuration file with "theme" set to "test-theme"
-    And I have an "index.md" page that contains "{{ site.test_theme.skin }}"
-    When I run jekyll build
-    Then I should get a zero exit status
-    And the _site directory should exist
-    And I should see "aero" in "_site/index.html"
-
-  Scenario: Disabling import of theme configuration entirely
+  Scenario: Enabling import of theme configuration
     Given I have a configuration file with:
       | key                 | value      |
       | theme               | test-theme |
-      | ignore_theme_config | true       |
+      | import_theme_config | true       |
     And I have an "index.md" page that contains "{{ site.test_theme.skin }}"
     When I run jekyll build
     Then I should get a zero exit status
     And the _site directory should exist
-    And I should not see "aero" in "_site/index.html"
+    And I should see "aero" in "_site/index.html"
 
   Scenario: A pre-configured theme with valid config file overriding Jekyll defaults
     Given I have a configuration file with "theme" set to "test-theme"

lib/jekyll/site.rb

@@ -432,7 +432,7 @@ def collections_path
     private
 
     def load_theme_configuration(config)
-      return config if config["ignore_theme_config"]
+      return config unless config["import_theme_config"] == true
 
       theme_config_file = in_theme_dir("_config.yml")
       return config unless File.exist?(theme_config_file)