[php:core] add Main option commonTempPath

## commonTempPath
Temp directory path for working place.

It will be encouraged to set up outside the document root.

**Data type:** string  
**Default value:** `'./.tmp'`

php/.tmp/.htaccess

@@ -0,0 +1,2 @@
+order deny,allow
+deny from all

php/elFinder.class.php

@@ -63,6 +63,13 @@ class elFinder {
 	 */
 	protected static $base64encodeSessionData = false;
 	
+	/**
+	 * elFinder common tempraly path
+	 *
+	 * @var string
+	 **/
+	protected static $commonTempPath = '';
+	
 	/**
 	 * Session key of net mount volumes
 	 * @var string
@@ -296,6 +303,10 @@ class elFinder {
 		$this->netVolumesSessionKey = !empty($opts['netVolumesSessionKey'])? $opts['netVolumesSessionKey'] : 'elFinderNetVolumes';
 		$this->callbackWindowURL = (isset($opts['callbackWindowURL']) ? $opts['callbackWindowURL'] : '');
 		self::$sessionCacheKey = !empty($opts['sessionCacheKey']) ? $opts['sessionCacheKey'] : 'elFinderCaches';
+		elFinder::$commonTempPath = (isset($opts['commonTempPath']) ? $opts['commonTempPath'] : './.tmp');
+		if (!is_writable(elFinder::$commonTempPath)) {
+			elFinder::$commonTempPath = '';
+		}
 		
 		// check session cache
 		$_optsMD5 = md5(json_encode($opts['roots']));