New api doc design

This PR shows the modifications made to the API doc for design purpose. To achieve this, the custom Sphinx theme Read The Docs (RTD) has been used.

Here is a [demo](http://docs.readthedocs.org/en/latest/theme.html)

Here is the new api design (link activated soon): 
[Test Link](http://mf-chsdi3.int.bgdi.ch/gal_doc_new_skin/)

Some adjustments were needed, as follows:

- adding relationship with a new custom.css file that basically formats RTD while required
- changing titles decoration for the sake of consistency 
- swisstopo.css, warning.png were deleted because no longer needed

More specifically:

buildout.cfg: 
- using now shpinx new version and RTD

custom.css: 
- body {word-wrap}: breaks strings (links and text in boxes) going beyond the page frame
- td{padding-left}: inserts spaces between numbers and text in 'Which layers are available/queryable/searchable?' topics
- #free/notfree/queryable/searchable {font-size}: text better fits the page frame

terms_of_use.rst: 
- allows insertion of Terms of Use in navigation bar

index.rst:
- inserting an hyperlink for 'Terms of Use'
- adjusting margins in 'Which layers are available/queryable/searchable?' topics

migration.rst
- inserting hyperlink for 'Github source code'

quickstart.rst
- switching old-fashion black frame to a sphinx note

conf.py
- imports shinx theme
- forces sticky navigation for the sidebar => not perfectly working (e.g. for Release notes)

index.rst
- improving map frame design
- adds warning about layer accessibility information
- removing Indices and Tables from toctree index

services/sdiservices.rst
- sphinx equation seems to not support long equation, no way found to autobreak equations 

setup.py
- adds shinx RTD

********************
Remaining bugs to fix:
-  problems with sticky navigation with the sidebar (e.g. for Release notes)
- Some elements of the sidebar are vanishing while playing with some of them, but only in Chrome, (e.g. click on Migration from API 2.0 guide > click on API Services then move cursor on the sidebar)