New Feature: Select destination folder when adding new transfer.

Hi,

First of all, I use your app every day. It allows me to add new torrents from magnet links. I love it.
But one thing I've been missing is the ability to select the destination folder in which the transfer will be added.
As an Android developer myself, I decided to develop this feature this morning and here it is.
How it works:
When adding a transfer from URL (from intent filter or through the + action bar item), you have a "Destination" button below the extract checkbox. The design is not final, maybe a label saying "Destination:<the destination>" with a "Change" button would look nicer...

![screen shot 2014-09-13 at 2 45 27 pm](https://cloud.githubusercontent.com/assets/1479283/4262136/8225e710-3b8f-11e4-87f7-9e065df612fb.png)

When you click on this button it opens a dialog with the file structure so you can select the destination folder you want. (I reused your Files fragment and made it a DialogFragment + some tweaks).

![screen shot 2014-09-13 at 2 45 37 pm](https://cloud.githubusercontent.com/assets/1479283/4262143/b3929c76-3b8f-11e4-84a0-82de72409d8b.png)

You can navigate through the file structure as you can do it in the main screen, and when you've chosen the folder you want, you can press the "Choose Folder" button.

![screen shot 2014-09-13 at 2 46 37 pm](https://cloud.githubusercontent.com/assets/1479283/4262147/d4b8ab20-3b8f-11e4-8946-cd79b7184972.png)

Once you clicked on that button, the dialog closes, and the selected folder is saved so it will be used in the API call (see the save_parent_id attribute in https://put.io/v2/docs/transfers.html#add).

![screen shot 2014-09-13 at 2 46 46 pm](https://cloud.githubusercontent.com/assets/1479283/4262150/03001c98-3b90-11e4-96af-5e1786d67391.png)

The only issue as you can see is that I couldn't find a way to get the name of the selected folder (there is a Files.getCurrentFolderId but no Files.getCurrentFolderName or Files.getCurrentFolder). 

Would you be able to help me on that?

Thank you in advance for your time. And thanks again for this awesome app!