Docs: Align presentation with TF-A

This patch adjusts the index and configuration used
for user-guide generation. It is aimed at helping
render the documents in a similar fashion to TF-A
documentation

* A trustedfirmware logo has been set
* TF-M abbreviations  have been expanded
* Menu navigation is now manually sorted
* Added license to the table of contents
* Disabled collapse_navigation in html_theme_options

Change-Id: I1cabff549a7c34bdb5c7a1da81addf3be094b6a5
Signed-off-by: Galanakis, Minos <minos.galanakis@arm.com>