instalation on subdirectory support added 1st stage

[callingmybluff]

Pull Request Summary

This is the first stage into implementing the feature #90.
This step replaces most static usage of root directory to an environment variable APP_LOCATION

However, with this PR, the feature is not done, and there are two issue I encountered and could not solve so far:

• When a url has a redirect, like login: /sub/admin/login?redirect=%2Fadmin will direct into /admin

• resources from the upload directory "uploads" are links in the page to /uploads/... instead of /sub/uploads/....

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[claviska]

Thanks for submitting.

When a url has a redirect, like login: /sub/admin/login?redirect=%2Fadmin will direct into /admin

This may point you in the right direction.

resources from the upload directory "uploads" are links in the page to /uploads/... instead of /sub/uploads/....

I think the problem here is that the editor generates root-relative URLs. I'm not sure what side effects we'll incur by changing it to relative. It's worth experimenting with at least.

[callingmybluff]

I managed to do the redirect easily, but the images thing is a bit tough. I managed to change images in display while input, but that resulted in problems (storing wrong url probably?)

[kylechine]

I don't know if this is annoying. But I just want to say thank you, guys.