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.

The table headers now have dragable resizing and the server
browser now have tags column. There's also right-click on
the header to show/hide columns.

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
* More columns parity to legacy browser

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