Added admin notice when Imagick is not installed

[igmoweb]

Imagick is needed to use this plugin, however it is not always installed.

I've added an admin notice to display an error message when the module is not available. There are certain things that could be also improved and discussed regarding this:

• Should JPEG\data_for_file() return an error when the module is not available?
• WP CLI just displays an standard The site is experiencing technical difficulties error when Imagick is not installed. It took me a while to realize what was the problem. Should we also add an error message for WP CLI?
• Should the notice be dismissable?

[roborourke]

Should JPEG\data_for_file() return an error when the module is not available?

I think we should just avoid bootstrapping the plugin at all apart from the admin notice in this case.

WP CLI just displays an standard The site is experiencing technical difficulties error when Imagick is not installed. It took me a while to realize what was the problem. Should we also add an error message for WP CLI?

Yeah I reckon that'd be helpful.

Should the notice be dismissable?

I think that's not super important, you either have Imagick or you don't, if you don't then you should probably be removing or deactivating the plugin.