non selectable and non commandable units

Added two booleans to a unit.

1. **selectable	|** if this is false, you cant select the unit.
2. **commandable	|** if this is false, you cant give the units commands.

I advise to set a non-selectable unit to non-commandable too if you want to make a normal unit morph into it.

This is mainly made for the spawn attack, because you may want for example spawn bees in a beehive which you are not able to select or control. I also recommend to accept my other pull request about the spawn attack together with this one.

New Syntax:
```xml
<unit>
	<parameters>
                ...
		<time value="25"/>	
		<multi-selection value="true"/>
		<selectable value="true"/>
		<commandable value="false"/>		
		<cellmap value="false"/>
		<levels/>
                ...
	</parameters>
...
</unit>
```