Making each package pt-docs capable (refs #9502)

* adding conf.py to src/docs - this is symlinked in all docs/eea.*
  sources in order to make them individual sphinx roots

* adding Makefile to src/docs - also symlinked in all docs/eea.*. The
  make command requiring this file is invoked from the new
  build-templates script

* adding build-templates script which parses src/docs/ for eea.*
  directories and makes the plone-pt target for each of them

* adding labels to eea.exhibit, eea.app.visualization and eea.googlecharts API.rst

* updating eea.daviz api/index.rst with conditionals depending on build
  type:

    * when html documentation is generated for use in eea.github.com,
      eea.exhibit, eea.app.visualization and eea.googlecharts will be
      referenced using :doc: and point to the path relative to src/

    * when plone-pt documentation is generated, the eea.* packages will
      will be referenced with :ref: via labels
Smarter template builder (refs #9502)
Adding --package option (refs #9502)
Updating builder (refs #9502)

Removing unnecessary configs
Adding makefiles (refs #9502)
Adding Makefile and build scripts (refs #9502)

* adding static Makefile
* adding build script, makefile needs to be called using this script
* updating documentation
Updating documentation (refs #9502)
Updating intersphinx eeadocs reference (refs #9502)
Updating howto (refs #9502)
Merge pull request #3 from hman/sphinx

Updating the way documentation is generated (refs #9502)