#275 Generate thumbnail images for documents stored on disk / CouchDB

[Amiel Elboim]

Generate preview thumbnails for images to improve loading speed.

New Globals configuration parameters:

1. Generate thumbnail – it's a boolean field, if it's false thumbnail feature won't work. (by default it's false).
   Thumbnail size – maximum size of thumbnail both X and Y dimensions. (the generator calculate this by the 2. image type (vertical or horizontal) ).

Functionality.

This generator uses PHP GD functions to make thumbnails.

If Generate Thumbnails set to On, all uploaded images will be saved in 2 copies: an original file for download , and a thumbnail for presentation.

There is option to present original image by adding additional parameter to reterive document url (http://localhost/main_openemr/openemr/controller.php?document&retrieve&patient_id=&document_id=) .
New parameter - 'show_original=true' (in the end of all parameters).

Limitations:

1. Generate for images only, can't generate PDF / Word thumbnail yet.
2. This feature can't generate thumbnail when encrypted file is uploaded.
3. Generator for existing files

For backward compatibility we included a possibility to generate missing thumbnails.

New button in Administration->Files category to start thumbnail generation for all images, this view returns all failed files.

https://github.com/openemr/openemr/pull/133