Update doxygen.cfg file, extract its HTML/CSS files

Update doxygen.cfg file, extract its HTML/CSS files

[Feature]       Doxygen cfg file was updated to 1.8.6
[Cause]         Warnings during parsing
[Solution]      Upgraded doxygen cfg with doxygen -u
[Verification]  Generate documentation - no warnings related to deprecated
                doxygen.cfg parameters should occur (these appeared at the very
                beginning of parsing; keep in mind - Vasum comments do produce
                warnings and will be fixed further on).

The commit additionally extracts default HTML header and footer, and default
CSS schema. These are kept in doc folder together with doxygen.cfg. Doxygen was
set up to use these files when generating documentation.

Change-Id: Ie8f78f0617e42de5bcaa6ce75b46cb436d3c8fd3