Hexen|Debug: Added assert() to catch a particle in NULL sector

Relates to bug: https://sourceforge.net/tracker/?func=detail&aid=3496963&group_id=74815&atid=542099
Dedicated Server: No need to calculate reverb parameters

A dedicated server is playing no audio.
Controls|Fixed: Walk and Sidestep must be clamped to -1…1 range

Otherwise, when moving with an offset axis (such as the mouse), the values
produce inconsistent movement.

Addresses bug: https://sourceforge.net/tracker/?func=detail&aid=3506285&group_id=74815&atid=542099
Input: Added a todo comment

Axis position filtering is presently missing.
Refactor: Relocated de::Plane's ddmobj_base_t sound origin to de::Surface

All map surfaces including planes and wall sections are modelled
using de::Surface. By relocating the sound origin to the surface
it will be possible to extend the existing sound manager to play
sounds originating from wall sections in addition to sectors and
planes.

Todo: The existing sound packet type(s) have fully utilized the
single byte which encodes the sound origin flags. We now need to
add an additional 3 flag bits for the wall surface origins...
Cleanup: Updated serverside sound management using current coding practices
Added: Initialize and update all map surface sound origin coordinates

Surface sound origin coordinates for all map surfaces are now set up
during map load and updated as necessary when a plane moves.

Updated serverside sound management for surface sound origins.

Todo: Replace the sound packet transmitted to clients with a revised
format suitable for use with any origin.
Added: Sound origin debug visual [cvar] rend-dev-soundorigins

Simple visual aid intended for debugging sound origins at runtime.
A label is drawn for each sound origin relative to its location in
the map.

A 3-bit bitfield: 0x1= Sector, 0x2= Plane, 0x4= SideDef
Fixed: Do not render particles in a NULL sector

Addresses bug: https://sourceforge.net/tracker/?func=detail&aid=3496963&group_id=74815&atid=542099
GL|Fixed: Disable texture NPOT if the ARB extension is missing

The texture NPOT GL feature was not being disabled if the required
ARB extension was missing. The feature was only disabled with the
command line options.

Fixes the issue of a fully white main menu background screen,
missing game UI fonts and psprites.
Merge branch 'master' of ssh://deng.git.sourceforge.net/gitroot/deng/deng
libdeng2: Copyright update
Homepage|Add-on Repository|Fixed: Errant HTML formatting in the notes field

Presently the add-on repository does not support embedding HTML in
the XML file used to define the add-on list.
Merge branch 'master' of ssh://deng.git.sourceforge.net/gitroot/deng/deng
Refactor: Renamed sidedefsection_t as SideDefSection and moved to public API

Note that the indices of the sections have also been changed to match
those used by the games when serializing material change thinkers to
saved games. The order of which does not matter as far as the engine
is concerned.

Also added an API helper macro for converting a SideDefSection to the
equivalent DMU property modifier flag.
libcommon: Added dmu_lib macro aliases for SideDef surface sound origins

Also renamed the existing aliases in line with current conventions.
libcommon|Refactor: Replaced sidedefsurfaceid_t with SideDefSection

Also updated p_switch.c/h in line with current coding practices.
API: Added DMU properties DMU_FLOOR_PLANE and DMU_CEILING_PLANE

Pointers to a sector's floor and ceiling planes can now obtained
with P_GetPtrp(), for example; P_GetPtrp(sector, DMU_FLOOR_PLANE)
libcommon|Refactor: Commonized map sound interface

Merged the functionality from each games' p_sound.c/h into common
source files in libcommon.

Reworked sector sound start interface, splitting the plane origin
selection out of P_SectorSound() and into the new function named
P_PlaneSound(). Behavior is unchanged, i.e., playing a sound from
a plane origin via this interface will automatically stop sounds
playing from other origins in the same sector.
libcommon: Add new source files p_sound.c/h