Fix image hover preview to work for gifv and imgur galleries

[Salgat]

For .gifv for example, it will try to load it since it sees the ".gif" extension, then fails. For galleries, perhaps allow for scroll wheel to navigate them.

[Salgat]

Pull request #24 partially fixes this issue. Still need to add gallery support.

[Salgat]

Need to also add support for gfycat