Implement a basic versioning configuration. Only a on/off switch for now.

I changed my mind about the more complex configuration options. We go with good default for now and don´t expose all the technical options to the users.
They can still override in the config file if it´s really really needed and they know what they are doing

apps/files_versions/js/versions.js

+$(document).ready(function() {
+        $('#versions').bind('change', function() {
+                var checked = 1;
+                if (!this.checked) {
+                        checked = 0;
+                }
+                $.post(OC.filePath('files_versions','ajax','togglesettings.php'), 'versions='+checked);
+        });
+});
+
 $(document).ready(function(){
 	
 	// Add history button to files/index.php

apps/files_versions/templates/settings.php

-<form id="external">
+<form id="versions">
         <fieldset class="personalblock">
-		<strong>Versions</strong><br />
-
-		Configuration goes here...
+	        <input type="checkbox" name="versions" id="versions" value="1" <?php if (OC_Config::getValue('versions', 'true')=='true') echo ' checked="checked"'; ?> /> <label for="versions"><?php echo $l->t('Enable Files Versioning'); ?></label> <br/>
         </fieldset>
 </form>