Add ability to set transferred file name

[claudiodangelis]

As per a private conversation with an user, it would be useful to have the possibility of specifying the name of the transferred file.

For a single file:

qrcp send MyFile.pdf --name attachment.pdf

For multiple files:

qrcp send MyFile1.pdf MyFile2.pdf --name attachment.zip

Open questions:

• should the file extension be automatically added?