Provide a dependency database/repo

[zulu]

Hi,

thanks for this great project. Flatpak is great for users – it enables
them to install/update new software without hassle. However, for a
developer, it‘s currently pretty hard to build software that depends on
other software. My project Mailnag for example depends on gtk3, python2
and 11 (!) other libs which in turn depend on further libs. I don‘t
think devs will accept that they have to read through all the build
instructions and configure/makefile switches (--enable-feature-x) of
each and every dependency. Currently the traditional approach of just
specifying package names of  ready-to-go dependencies in packaging
toolchains for the developer’s favorite distros seems to be far more
convenient. 

As a solution I propose to provide a dependency database or repository
that contains „dependency recipes“ for frequently used dependencies
like python, gtk etc. Something similar to Arch Linux‘ AUR. This way, a
developer simply has to specify the dependency names (like
dependencies: gtk, python) in the json file and flatpak builder would
look up the nasty details (like official download location, checksum,
build commands and switches). Ideally there should also be a way for
developers to upload/review/comment new recipes. I guess this approach
would also stop all the please-provide-a-runtime-for-dependency-x
requests for good.

Regards
Patrick