Improve placement preview mouse position handling

[mharis001]

When merged this pull request will:

• title, fix issue with RscDisplayCurator_mousePos unexpectedly updating when mouse is over mission controls group

Relevant code from RscDisplayCurator.sqf:

//--- Mouse area
{
	_ctrl = _display displayctrl _x;
	_ctrl ctrladdeventhandler ["mousemoving","with (uinamespace) do {RscDisplayCurator_mousePos = [_this select 1,_this select 2];};"];
	_ctrl ctrladdeventhandler ["mouseholding","with (uinamespace) do {RscDisplayCurator_mousePos = [_this select 1,_this select 2];};"];
} foreach [IDC_RSCDISPLAYCURATOR_MOUSEAREA,IDC_RSCDISPLAYCURATOR_MISSION];