fix contributors file, re-arranges scripts structure and requirements

CONTRIBUTORS.md

@@ -18,6 +18,8 @@
 # Contributors
 
 - **[Victor Salimonov](https://github.com/VikTorSalimonov)**
-- **[Sebastián Yonekura](https://github.com/syonekura)**
-
   * Documentation, screencasts
+
+- **[Sebastián Yonekura](https://github.com/syonekura)**
+  * [convert_to_voc.py](cvat/utils/convert_to_voc.py) - an utility for 
+  converting CVAT XML to PASCAL VOC data annotation format.

cvat/requirements/base.txt

@@ -22,4 +22,3 @@ scipy==1.0.1
 sqlparse==0.2.4
 django-sendfile==0.3.11
 dj-pagination==2.3.2
-pascal-voc-writer==0.1.4

cvat/utils/requirements.txt

@@ -0,0 +1 @@
+pascal-voc-writer==0.1.4