New fixture

Added new fixture: Showtec Phantom 25/50
Updated File open icon and TODO
Merge pull request #50 from Petja/ff2f59a42fedbd8e8de390f5bdba869ad97e8eb3

Added fixture: Showtec Phantom 25/50
Added Showtec Phantom 25/50 to project
Added fixture: Showtec Phantom 50 (thanks to Petja Touru)

Updated changelog and advanced to version 4.2.1
Added fixtures list import/export feature to shorten projects creation
Added toolbar icon to Scene Editor and Chaser Editor to Show/Hide Speed Dials window (default: hidden)
Improved Speed Dial window visibility from Chaser Editor

Improved import/export icons
Updated translations
Added ArtNet input support (tested on Android with Art-Net controller LITE and Controlador Artnet-DMX)

Since QLC+ is polite, it now responds to ArtNet Poll requests
Improved Speed Dial icon
Improved ArtNet configuration panel when an interface is no longer available

Show only available Inputs/Outputs on Input/Output Manager
ArtNet code improvement to correctly handle input/output indexes