NeoUI - Table headers + main table API + section X-axis scrolling

NeoUI table headers and main table API implemented, now have
Begin/EndTable and NextTableRow implementation replacing the
previous custom paint + button. Now can just layout the table
cells with widgets, although at the moment only NeoUI::Label
are properly utilized and dealt with. Other widgets are not
refactored up for tables yet.

Sections now have X-axis scrolling, mainly used for table and
header scrolling support.

OTHERS:
* Fix SDR/Steam networking server bot vs player number count
* Fix border in smaller resolutions

TODOs:
* Fixup tab X scrolling
* Section X-scrollbar controls options/flags
  * Modes:
    * No X-scrollbar
    * Indicator/thin X-scrollbar
    * Dragable/thick X-scrollbar
  * Using BeginTable will automatically put
    the section into Dragable/thick X-scrollbar
    mode
* Some TODOs in source code
  * Extra filtering
  * Change from only header to any sections to reference other
    section's scrolls

FUTURE TODOs:
* Refactor painting of widgets to utilize vgui viewports
* Possible split of painting (and colors) from NeoUI internals
* Vertical layouting that expands horizontally as oppose to the
  default horizontal layouting that expands vertically

* fixes #1566
* fixes #994
* fixes #1815

Author: nullsystem