Weapon (aiming/shooting) editing and debugging #107

Conversation on the current state of weapon debugging:
<[S44]FLOZi> there is a tool in /debug to show weapon cones
<[S44]FLOZi> but
<[S44]FLOZi> it only shows in certain circumstances
<[S44]FLOZi> only when attack command is the active player command and unit is selected
<[S44]FLOZi> so a similar thing that shows e.g. maindirs + maxangledif
<[S44]FLOZi> http://i.imgur.com/gEMSfmd.png
<[S44]FLOZi> http://i.imgur.com/msWGt2o.png
<[S44]FLOZi> https://springrts.com/wiki/Gamedev:DebugDrawModes

It would be useful if we could also provide on-the-fly editing so we don't have to go through the process of edit->restart spring (likely to require engine changes).
We might need additional information that tell us why the aiming/shooting fails and what is going on.

PS: Worth invoking @FLOZi for further feedback.