Changed sphinx documentation theme to ReadTheDocs theme

Theme can be found at: https://github.com/snide/sphinx_rtd_theme

Change-Id: I48c234326a8db6a053438296e65cd2f2957cf485
Removed common documentation and added servermanager proxies page

* Removed the PARAVIEW_DOCUMENTATION_SKIP_ADD_FUNCTIONS workaround
* Removed common documentation pieces originating from CreateObject method
* Exclude generated proxy documentation from simple module doc page
* Created a new page that lists/summarizes all generated proxy documentation
* Interlinked the two pages to be able to navigate between the two
* One page per generated proxy
* Documentation generated by instantiating each generated proxy class which
  causes a whole bunch of warnings and errors since it will be instantiated
  without any arguments

Change-Id: I9cfb26d74ad4094373ae84b581bd13761621226c
Added pydoc output parser to generate docs for proxies

Using servermanager.[xxx].proxy for pydoc help generator
[xxx] being one of ['filters', 'sources', 'writers', 'animation']

Change-Id: I0396e312be41a75900f2c94a811c8e7c8685fc6f
Improved theme styling

* Enabled text-wrapping for servermanager proxies page
* Made sure toctrees render only upto 1 level of hierarchy in the sidebar
* Added ParaView logo to sidebar
* Added Index link to the header
* Added current version under logo
* Improved section headings and toctree hierarchy

Change-Id: I6de43b4d492009414996fa0d153a53108c52ae05
Merge topic '14381_sphinx_doc_generated_classes' into next

b432f6e Improved theme styling
52e1b82 Added pydoc output parser to generate docs for proxies
5305521 Removed common documentation and added servermanager proxies page
29c8b68 Changed sphinx documentation theme to ReadTheDocs theme