Remove built dependencies

[kaedroho]

This commit removes libsass and Pillow from the setup.py dependency list. This greatly improves install performance and also means that the basic Wagtail installation is pure-python (so no build tools need to be on the end users host machine).

None of these dependencies are directly called from within Wagtail so the start project command continues to work correctly.

[zerolab]

Hi @kaedroho,

Can you add a paragraph in the documentation for the use case outlined by @gasman in #958 (comment). That is if Wagtail is added to an existing Django project rather than starting a new project using the template.

It also looks like #958 has an unanswered question from @tomdyson. Although it may be the case you already discussed this offline.

[gasman]

+1 for removing them as dependencies of the wagtail package itself, but we need to do a proper job on the documentation - removing all reference to them is not sufficient, because not everyone's using Vagrant, and for those people the dependencies are just as necessary as they were before.

If anything, our documentation now needs to be more explicit about the dependencies, because an error during package installation made it pretty obvious that some prerequisites were missing, whereas a failure during site setup is likely to lead people to assume that Wagtail is broken. I think this is going to require a fairly major rethink of the docs, to convey all the relevant information: "this is how far installing the wagtail package is going to get you; these are the dependencies your site is going to need; here are some options to save you the hassle of installing them" etc.

[SalahAdDin]

But, if now we haven't libsass, how you put all scss styles in wagtail admin?

[gasman]

@SalahAdDin We aren't dropping libsass. This is just about reorganising the way we specify dependencies in the code, so that people using virtual machines (such as Vagrant) only have to install libsass within the VM, not on the host machine.

[gasman]

Sorry, but I think we need to revert this. In the last week I've had two Torchbox sites fail to install cleanly with vagrant up because their requirements.txt files were missing these libraries - and if that's a problem on our own sites, it's going to be ten times worse when we have to troubleshoot other people's.

Having to install native dependencies on the host machine is annoying, but people have dealt with it up to now, and we have 8 releases worth of experience in dealing with those problems. It feels like we've rushed into this change without fully thinking through the implications, and the result is that we're adding another layer of "stuff that can go wrong". We're going to have our hands full dealing with support queries from the rest of the changes in 0.9 - this is an extra problem that we could do without. (And hopefully the next release will then have a proper solution for libsass - #35 (comment))

[davecranwell]

Sounds sensible.

[gasman]

re-closing, as this is now reverted.