Update license.

This is important now that we're using tmhOauth, which is released
under the Apache 2 license and is *not* compatible with GPL2.
Tweak showcase presentation.
Use wp_register and wp_enqueue functions consistently.
Remove <hr> from webcomic media modal display.

Also shorten the message display time.
Update image context for collection posters.
Enhance the Webcomic Link widget and add additional link widgets.

New widgets include Webcomic Collection Link (which uses the new
webcomic_collection_link() template tag), Webcomic Storyline Link, and
Webcomic Character Link.
Use WP_Http instead of curl() for API and Paypal requests.
Force showcase image dimensions.
Add $debug property.

May be useful for toerh uses in the future, but right now setting
$debug to `true` switches to the PayPal sandbox for testing.
Replace logfiles with webcomic_commerce custom post type.

This avoids any need to write files to the server, and might make the
logs even more useful in the future.
Add Widget_PurchaseWebcomicLink, refactor existing widgets.
Update license to GPL3.

This has technically been the case since switching to tmhOauth, which
uses the Apache 2 license and thus requires GPL3.
Remove April Fool's script.
Update admin page icons.
Remove stray token.
Update Twitter API

Correct calls to version 1 of the API so they point to version 1.1.
Add link to review plugin.
Add new widgets and update media features.

Add Webcomic Print, Scheduled Webcomics, and Webcomic Transcripts Link
widgets. Also streamline media features.
Correct network creator regex.
Correct webcomic post archive integration.

Previously this did not account for other custom post types. Fixes #158