Add getClassesInTime API method

This API method allows for a client to get the classes which took/will
take place at a specific time.

commit c69382ea8fe906d9d5ca783adb9e955163f4098e
Author: Sergi Soler 'fraret <fraretblauet@gmail.com>
Date:   Sun Oct 4 12:50:57 2020 +0200

    Changed getClasses in time to POST and fixed very minor issues with latest commit

commit 19f9688a16fe1de667f02c0f33b7375b51356d13
Author: Sergi Soler 'fraret <fraretblauet@gmail.com>
Date:   Sat Oct 3 14:54:24 2020 +0200

    Added option to get Classes at specific time

Close #1

Co-authored-by: Sergi Soler 'fraret <fraretblauet@gmail.com>
diff --git a/inc/API.php b/inc/API.php
index 8ecfdd1..1eac89f 100644
--- a/inc/API.php
+++ b/inc/API.php
@@ -145,7 +145,22 @@
 
       case 'getCurrentClasses':
         self::checkRequestMethod('GET');
-        $classes = Classes::getCurrentClasses();
+        $classes = Classes::getClasses();
+        if ($classes === false)
+          self::returnError();
+        else
+          self::returnPayload([
+            'classes' => $classes
+          ]);
+        break;
+
+      case 'getClassesInTime':
+        self::checkRequestMethod('GET');
+        if (!$parts[1]) self::returnError("You must provide a unix time");
+        $unix_time = filter_var($parts[1], FILTER_VALIDATE_INT);
+        if (!$unix_time) self::returnError("Received parameter is not an integer");
+
+        $classes = Classes::getClasses($unix_time);
         if ($classes === false)
           self::returnError();
         else