Add setting option for download location

[Theblackcat98]

trafficstars

As the title states, I think it would be a welcome addition to be able to change the default download location for books.

[Asmageddon]

Yeah, this looks much better as a frontend/downloader than as a reader tbh.

[dstark5]

Yeah sure will add it in the future updates

[shuvashish76]

Duplicate of #32 isn't it? Close one of the issue.