Allow disabling all bundled libraries

[jtojnar]

Could you add an option for disabling the rest of the bundled libraries? At least BUNDLED_RAWSPEED or even BUNDLED_ALL

[aferrero2707]

In the current stable branch all bundled libraries are optional, and disable by default. The only exception is RawSpeed, for two good reasons:

• it is not provided as a separate package in most Linux distributions
• the list of supported RAW files is considered part of the specific characteristics of a given release, and is not supposed to change from one system to another. That's the main reason why I am against using a system-provided RawSpeed library, and on this I follow the logic of the Darktable developers...

By the way, thanks for bringing Photoflow into NixOS! I would really encourage you to consider having "bleeding edge" builds from the stable branch in addition to the 0.2.8 release, as they are likely to be even more stable...

At the moment I am still far from being ready for a new major release.