[php,cmd:open] fix #1586 RFC7233 violation, add commandsOptions.open.method

- php:connector - range request supports on GET request only
- js - add an option `commandsOptions.open.method`
```javascript
open : {
	// HTTP method that request to the connector when item URL is not valid URL.
	// If you set to "get" will be displayed request parameter in the browser's location field
	// so if you want to conceal its parameters should be given "post".
	// Nevertheless, please specify "get" if you want to enable the partial request by HTTP Range header.
	method : 'post'
},
```

php/elFinderConnector.class.php

@@ -27,7 +27,13 @@ class elFinderConnector {
 	 **/
 	protected $header = 'Content-Type: application/json';
 
-
+	/**
+	 * HTTP request method
+	 * 
+	 * @var string
+	 */
+	protected $reqMethod = '';
+	
 	/**
 	 * Constructor
 	 *
@@ -38,6 +44,7 @@ class elFinderConnector {
 	public function __construct($elFinder, $debug=false) {
 		
 		$this->elFinder = $elFinder;
+		$this->reqMethod = strtoupper($_SERVER["REQUEST_METHOD"]);
 		if ($debug) {
 			$this->header = 'Content-Type: text/html; charset=utf-8';
 		}
@@ -50,8 +57,8 @@ class elFinderConnector {
 	 * @author Dmitry (dio) Levashov
 	 **/
 	public function run() {
-		$isPost = $_SERVER["REQUEST_METHOD"] == 'POST';
-		$src    = $_SERVER["REQUEST_METHOD"] == 'POST' ? $_POST : $_GET;
+		$isPost = $this->reqMethod === 'POST';
+		$src    = $isPost ? $_POST : $_GET;
 		if ($isPost && !$src && $rawPostData = @file_get_contents('php://input')) {
 			// for support IE XDomainRequest()
 			$parts = explode('&', $rawPostData);
@@ -151,7 +158,9 @@ class elFinderConnector {
 		if (isset($data['pointer'])) {
 			$toEnd = true;
 			$fp = $data['pointer'];
-			if (elFinder::isSeekableStream($fp) && (array_search('Accept-Ranges: none', headers_list()) === false)) {
+			if (($this->reqMethod === 'GET' || $this->reqMethod === 'HEAD')
+					&& elFinder::isSeekableStream($fp)
+					&& (array_search('Accept-Ranges: none', headers_list()) === false)) {
 				header('Accept-Ranges: bytes');
 				$psize = null;
 				if (!empty($_SERVER['HTTP_RANGE'])) {
@@ -201,13 +210,16 @@ class elFinderConnector {
 			// client disconnect should abort
 			ignore_user_abort(false);
 
-			if ($toEnd) {
-				fpassthru($fp);
-			} else {
-				$out = fopen('php://output', 'wb');
-				stream_copy_to_stream($fp, $out, $psize);
-				fclose($out);
+			if ($reqMethod !== 'HEAD') {
+				if ($toEnd) {
+					fpassthru($fp);
+				} else {
+					$out = fopen('php://output', 'wb');
+					stream_copy_to_stream($fp, $out, $psize);
+					fclose($out);
+				}
 			}
+			
 			if (!empty($data['volume'])) {
 				$data['volume']->close($data['pointer'], $data['info']['hash']);
 			}