Add support for multiple files

[MateusRodCosta]

Currently the app only supports a single file, so it isn't shown on the share sheet when sharing multiple files.

Add support for the intent filter for multiple files as well as UI support for showing info and downloading multiple files.

[MateusRodCosta]

I have been thinking on ideas on how to do this.

The best one I thought so far is keeping the same DetailsActivity for receiving the intent (and the alias for it as well), but loading different UIs depending on the intent.

So, I would either load a many file UI and a single file UI. The many files UI would be some sort of list with all the items and a button to save all (or at least all selected) and clicking each item would take to the respective single file UI.

Not sure yet when I will implement this though, but since I now have an idea of what UI to do...

[nizhiyi]

it's useful to save as .zip for multiple files.