Automatic image ALT attributes

Restores WordPress default functionality prior to version 4.7 where image ALT attributes were automatically generated and put into the HTML code. The ALT attributes were generated from the Caption (if it exists) else from the Title (if it exists) of the image in the Media Library. This plugin utilises Titles in generating ALT text, but does not utilise Captions. The Title used by this plugin, is the main Title of the image as found in the Media Library, not the HTML TITLE attribute of the image (that is something else, which this plugin ignores).