ScissorRect for DModelPanel

Adds a scissor rect to the DModelPanel Paint hook which prevents the
drawn model from "leaking" outside of the area of the DModelPanel which
is being drawn.
Update gm_demo.lua

You can now disable the demo recording icon with gm_demo_icon.
Fix vehicle third person affecting cameras

When looking through camera, the vehicle third person affects view position. It shouldn't.
Improve DAdjustableModelPanel

* Adds CTRL and SPACE keys to lower or raise the camera position vertically
* LMB now rotates view around the model, holding SHIFT restricts movement to X axis. This isn't perfect, but it is still helpful.
Use Enums instead of numbers
Update spawnicon.lua

* Fixes clicking "Resize" automatically rerendering the icon.
* Remove all trailing whitespace and semicolons.
Fix weapon error with NPCs
Update sent_ball.lua

* Rebalanced size and visual size.
* Sound is lower pitch the bigger the ball is
Update Simple DOF

* Works properly with cameras
* Increased size for the sprites for higher FOVs
Improve properties system

* Now works when you look from camera/driving a vehicle
* Fixed some issues with "Drive" property and cameras.
* Added language string for "Undone_KeepUpright"
* Removed undo from keep upright property. You are supposed to use
properties to disable keep upright.
Remove Undo_KeepUpright
Update properties.lua
Added RemoveChangeCallback
Added identifier for AddChangeCallback and RemoveChangeCallback
Update menu.html

Fixed some HTML
Localize some variables

There's no reason for them to be global.
Update menu.html
Update menu.html
Update dimage.lua

Fix for PANEL:SetImage if you use two .png images
Update draw.lua

Fix retvals for draw.SimpleText and add retvals for draw.SimpleTextOutlined
Update errors.lua

Reduce time of Lua error notification from 30 to 10 seconds.