Changes/fixes to r_dynamic, cl_ambientsound, skulk walk speed, -attack

[pierow]

• r_dynamic is now client toggleable for non-nvidia graphics users experiencing performance issues
• cl_ambientsound changed to be client side. It previously changed some code on the server, causing ambient sounds to be off for all users on dedicated servers. Unfortunately, there is no way I can find to toggle .wav map ambient sounds via a client only cvar. This command toggles mp3 sounds which are generally the most annoying and offensive. Players that wish to remove all ambient sound will need to replace the offending .wavs with blank files as was in previous versions of the game.
• Skulk walk speed changed to give the skulk 140ups when slow walking as it was in v3.2 and earlier. It was mistakenly set to be too slow when those values were changed to address https://github.com/ENSL/NS/issues/68
• Releasing the attack bind should no longer cancel +movement