vastspace: Fix Soldier's client beginControl script haven't run

The logic is altered; isServer() == false doesn't necessariliy mean
isClient() == true.  Now we use the correct API call to determine
whether the beginControl script should be set.

Also hidden GLwindows when a Soldier is controlled just like surface
mod's Aerial classes branch.
vastspace: Add icon model for selected gun (assault rifle) for Soldier
vastspace: Add sniper rifle icon texture to indicate equipped weapon
vastspace: Add remaining rounds indicator for each firearm