v0.4.0

• Added ability to fetch images from various booru-like sites by url. Supported danbooru.donmai.us, gelbooru.com, rule34.xxx, yande.re, and safebooru.org. But also, there is a possibility that other websites with similar API to listed previously can work.
• Some changes to how tags work. It shouldn't change anything, but it's possible for some bugs to be fixed.
• Fixed a bug where images were saved in wrong format.
• Fixed group preview, tags now work properly.
• The tag "NSFW" isn't required anymore, but it still is the default tag.
• Little improvement to the image scaling in image preview.
• Added "id", "source", and "rating" fields to image info, and "id" to image groups.
• Added a button to open the source of an image in browser, if it has the source.