Add Pixiv Support

[ScreamingHawk]

Sharing from the Pixiv App includes some text about the image as well as the link. The link can be extracted and used

[ScreamingHawk]

Considering allowing user to store pixiv username / password and using loader if those are present

[ScreamingHawk]

https://www.programcreek.com/java-api-examples/?code=moeoverflow/PixivForMuzeiPlus/PixivForMuzeiPlus-master/app/src/main/java/moe/democyann/pixivformuzeiplus/util/Pixiv.java