Added Reflector Cask

This adds a cask to install Reflector by Airsquirrels.
Their download link always points to the latest version,
hence no hash as that would break when they update.
When first launching after installation the app will
request to be copied into /Applications rather than run
from ~/Applications.
Renamed cask Reflectorapp to Reflector

Rightfully suggested by NanoXD that the application is called
Reflector and not Reflectorapp. Naming change to align with
naming conventions.
Merge pull request #1751 from henninghoyer/reflectorapp

Added Reflector Cask