Support soju.im/FILEHOST

[4e554c4c]

Soju's FILEHOST allows an irc client to upload files to a designated http host to share as hyperlinks. This avoids proxy issues that can limit DCC, and allows for automating the common process of uploading images / pastes to a file host and sharing them.

Existing implementations:

• goguma
• gamja

Implementing this would involve:

1. Supporting the soju.im/FILEHOST ISUPPORT token
2. Adding a UI button for uploading files
3. Adding code to check MIME Types and preparing files to upload