Do something with installing Pillow package

[jakubg1]

In order for the converter to work, Python needs Pillow, which is an image toolset library, and that does not come preinstalled with Python. This means that the user has to download Pillow using a package manager. So, for convenience, it is installed automatically, without even prompring the user.

The Python Package Index is not fully safe though; it contained quite a lot of malicious packages. If the Pillow library were to be compromised, its automatic installation could pose serious threats to the end user.

That's why automated installation is going to be removed.
Possible solutions are:

• Let the user manually install the package
• Prompt before installing the package in the actual script (I think this would be more user-friendly)