if LBM files missing

Some folks (me!) deleted some of their LBM files decades ago. Game should not raise an exception if they are missing.
Handle ctrl-key
support strafing sideways movement

properly resubmitted, I hope.
Tank, turn turret with ctrl-click

Implements "strafe" move for tanks, in which ctrl-click turns the turret. The tank subsequently moves with the turret strafed.
Merge branch 'game_h_cpp_handle_ctrl_key'
add shift-to-run
Merge branch 'running'
fix Sectopod weapon fire and hit sounds

They're supposed to be lasers as opposed to silence on fire and a zombie bite
on hit, I think...
fix for visible unit button
fix ICONS.PCK are res free
- removed unused NodeLink class, a nodelink is now just an ID(number) of the linked patrol node
Adding cancel button on New Game State to go back to main menu.
Fix for https://github.com/SupSuper/OpenXcom/issues/240 , misleading
error message.
proper handling for fatally wounded soldiers.
- Fixed OpenXcom not accepting Unicode paths properly.
- Fixed occasional crash in LBM loading.
Initial Blaster Launcher AI Code
fix base attack screen.

tested and working and marvellous.
kill more soldiers

because i hate you.
fixes for some bugs

lazy code
refactor AggroState