Refactor for 0.2

TODOs:

• Progessbar for the sender
• Improve text for incoming files in device list
• Replace g_print() with g_debug ()
• Remove dummy devices
• Add new avatar in About Dialog
• Remove server route after file download
• Show download error when file can't be downloaded/saved
• Automatically rename files if they exist already in the download folder
• Update App Id to com.juliansparber.teleport #45

cc: @bertob