Large CSS files included with every page load

Problem/Motivation

Whenever this module is enabled it includes the CSS files calendar_multiday.css and calendar.css with every page load, even if there are no calendars on the page. This is very wasteful and easy to fix.

Steps to reproduce

Use a browser's developer mode to look at the CSS files loaded with the page when CSS aggregation is turned off.

Proposed resolution

Remove the hook_page_attachments() implementation and only load the library when needed during theme preprocessing. Please see the attached patch.