Image & Video collection player imaplemented using orbit image slider

**Feature Enhancements**

* mid size images can be created from now onwards while saving any image files , previously it was not creating mid size images, in place of mid size image it was displayed full image itself.
code modified in ```file.py  --> convert_mid_size_image()```

*  For some images in DB there were no thumbnails created, for them thumbnails and mid size both are created by running script.

* Script (convert_mid_size_images.py) written for all images to create mid size images and for whom thumbnails was not created,  script creates thumbnails as well as mid size image according to the size of the image.

* Now mid size image is displayed on node's detail view page, previously it was showing full size image.

* removed unused scripts from base.html
   ```../ jquery-legacy / jquery-migrate.js```  and  
   ``` ../ jquery-legacy / jquery.min.js ```
(since now updated versions of those have been used in specific templates from bower)

* Query modified in ```get_drawers() --> methods.py``` for heterogeneous collection.
Now included only "Page, File and Quiz" elements in left drawer to build a resource collection.

   **collection manager enhancement:**

     * Now when user clicks on collection tab while editing any node, an overlay having two options appears to select, as homogeneos collection and heterogeneous collection.

     * When user clicks on homogeneous collection , it takes the current nodes type and only those types of resources gets populated in left drawer. for eg: if user edit any page , and selects homogeneous option, then user can see only pages listed in left drawer to build homogeneous collection. in the same way for images only images are visible in left drawer...and so on 

     * for groups condition added , such as for groups only heterogeneous collection should display.
 
   **Image and video gallary implementation:**

    * For image and video collections, orbit image slider implemented , which is default provided by foundation.

    * This image slider can only visible when you have images or video collections.

In this way we have satisfied nroer specifications for image and video collections. by providing an option to select homogeneous collection type.

**What is to test**
* Run command : **python manage.py convert_mid_size_images**
  (This will create mid size images for all images in your DB also creates thumbnails , it those are missing)

* Go to any page or any resource , then click on edit, click on collection tab, you will see two options on overlay such as , homogeneous collection and heterogeneous collection.

* check when you click on homogeneous collection, the current nodes type is get selected for homogeneous and display only that type of resources.

* When you click on heterogeneous collection, it will display heterogeneous elements in drawers and also you can select any homogeneous type from radio buttons as previous.

* Click on any image file and check that in details view mid size image is displaying or not.
 
* go to file app and create image collection or video collection and check if you can see the image slider view or not.