Added secure sign key generator command

[AndrewCarterUK]

I've added a command that can be used to securely generate keys.

This is a first draft and I'm just submitting for review.

andrew@laptop ~/Development/glide $ php bin/glide-console generate-sign-key
bGS6lzFqvvSQ8ALbOxatm7/Vk7mLQyzqaS34Q4oR1ew=

andrew@laptop ~/Development/glide $ php bin/glide-console generate-sign-key --format=hex
531a5187f08846a40ab6a9f9c651831bdd188e84b026804039773ef0aa51e500

andrew@laptop ~/Development/glide $ php bin/glide-console generate-sign-key --entropy=64
ladkecOLF7RvMl/J5EGr/SMz5InfSyX+DA9CvecE/OiVFndnMqgvfLofNGO6/Gc5P1Io+eHYhcJphIRHCB9Kpg==

[AndrewCarterUK]

I've re-factored this into it's own repository now (I saw another project that needed a similar utility).

Happy to leave this pull request up or alternatively you could recommend https://github.com/AndrewCarterUK/CryptoKey

I've got no issues either way :)

[reinink]

LOVE IT. But yes, I think as a separate package. Well done. I'm going to add this to the recommended packages list, and the documentation.

Thanks again, Andrew, for your help with making Glide more secure. VERY much appreciated.