www/pydio-cells: Fix build and overhaul

Summary:
Pydio cells uses a custom version of packr to embed the static
resources into the cells binary. Previously, the embedding process
was not peformed, resulting in a non-functional binary. When trying
to use the app, user will just get "404 Not Found" error instead of
a web page.

To fix this - before the build gmake generate has to be performed
in the WRKSRC, and a special custom version of packr v1
(devel/pydio-packr) has to be used.

Other changes:

• DOCS option was removed, as the README.md file didn't really provide any useful information for the port's users
• Generation of bash and zsh completion files was added
• App version is now provided during the build process (previously 0.1.0 would be indicated instead of the real version)
• Indicate failure to build on i386
• Create separate user/group for running the daemon, as recommended by the administrator's manual
• Add rc script
• Add pkg-message with configuration instructions
• Add more patches fixing bugs and adapting the code for FreeBSD

No UPDATING is required, as the port was not functional previously

Reviewed by: koobs
MFH: No (port isn't in any of the quarterly branches yet)
Differential Revision: https://reviews.freebsd.org/D30323