[TASK] Base DynTab on Bootstrap and re-color

Base the DynTab tabs on <ul> and Bootstrap nav-tab. Also
base the tab colors on Bootstrap variables and remove colors
as well as gradient.

Related: #62002
Releases: master
Change-Id: Ibff2f3633512538b323af465e55ef9d08fc8bfd3
Reviewed-on: http://review.typo3.org/33130
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
[TASK] Remove TBE_STYLES mainColors from PHP

TYPO3 uses $TBE_STYLES to define certain
variables like background colors in PHP that
can be overridden with extensions.

In order to streamline the rendering of the
backend that should completely done via
LESS / CSS, the corresponding PHP parts are
removed, as they should have no effect
anyway - this is already done via CSS.

Releases: master
Resolves: #62039
Change-Id: I81533c1d2912fc25b96f106974e5cd625b827c90
Reviewed-on: http://review.typo3.org/33168
Reviewed-by: Felix Kopp <felix-source@phorax.com>
Tested-by: Felix Kopp <felix-source@phorax.com>