application: refactor version checks, move to ApplicationUtils

Relates to #372

Modifications:
 - move checkUpdate() to ApplicationUtils
 - reduce file I/O operations during version checks
 - apply coding conventions
 - add test coverage

Tools:
 - create a sandbox directory for tests

Signed-off-by: VirtualTam <virtualtam@flibidi.net>

tests/CacheTest.php

@@ -11,10 +11,10 @@ require_once 'application/Cache.php';
 /**
  * Unitary tests for cached pages
  */
-class CachedTest extends PHPUnit_Framework_TestCase
+class CacheTest extends PHPUnit_Framework_TestCase
 {
     // test cache directory
-    protected static $testCacheDir = 'tests/dummycache';
+    protected static $testCacheDir = 'sandbox/dummycache';
 
     // dummy cached file names / content
     protected static $pages = array('a', 'toto', 'd7b59c');
@@ -56,7 +56,7 @@ class CachedTest extends PHPUnit_Framework_TestCase
     public function testPurgeCachedPagesMissingDir()
     {
         $this->assertEquals(
-            'Cannot purge tests/dummycache_missing: no directory',
+            'Cannot purge sandbox/dummycache_missing: no directory',
             purgeCachedPages(self::$testCacheDir.'_missing')
         );
     }