Feature/particle speed up

With this feature you can **speed up** particles.
For example with negative speed + spherical shape you can make very nice effects.

Syntax
```xml
 <speedUp constant="-0.03" relative="0.03"/>
 ```
Both are **optional** ( so you could do ```<speedUp constant="-0.03"/> ``` aswell ), but can be **combined** aswell.

Constant means that each cycle a percentage of the start speed is added
Relative means that each cycle a percentage of the current speed is added

Here are some Examples which you can see here:

Here are the Xmls of the Examples:
The "lines"
```Xml
<unit-particle-system>
    	<texture value="true" path="images/particle.bmp" luminance="true"/>
	<mode value="normal"/>
	<primitive value="quad"/>
	<offset x="-1" y="1" z="0.5"/>
	<direction x="0.03" y="0" z="0"/>
	<color red="1" green="1" blue="1" alpha="1" />
	<color-no-energy red="0" green="0" blue="1" alpha="1" />
    	<radius value="0" />
    	<size value="0.1" />
    	<size-no-energy value="0.4" />
    	<speed value="2.0" />
	<speedUp constant="0" relative="0.01"/> / <speedUp constant="0.01" relative="0"/>
	<gravity value="0"/>
    	<emission-rate value="0.5" />
    	<energy-max value="170" />
    	<energy-var value="0" />
	<relative value="true" />
    	<fixed value="true" />
    	<teamcolorNoEnergy value="false" />
    	<teamcolorEnergy value="false" />
</unit-particle-system>
```
The "ball":
```Xml
<unit-particle-system>
    	<texture value="true" path="images/particle.bmp" luminance="true"/>
	<mode value="normal"/>
	<shape value="spherical">
		<angle value="90"/>
	</shape>
	<primitive value="quad"/>
	<offset x="0" y="0" z="1"/>
	<direction x="1.0" y="0" z="0"/>
	<color red="1" green="1" blue="1" alpha="1" />
	<color-no-energy red="0" green="0" blue="1" alpha="1" />
    	<radius value="0.1" />
    	<size value="0.1" />
    	<size-no-energy value="0.4" />
    	<speed value="2.0" />
	<speedUp constant="-0.03" relative="-0.007"/>
	<gravity value="0"/>
    	<emission-rate value="0.5" />
    	<energy-max value="70" />
    	<energy-var value="0" />
	<relative value="true" />
    	<fixed value="true" />
    	<teamcolorNoEnergy value="false" />
    	<teamcolorEnergy value="false" />
	<alternations value="1" />
</unit-particle-system>
```
The "Ring"
```Xml
<unit-particle-system>
    	<texture value="true" path="images/particle.bmp" luminance="true"/>
	<mode value="normal"/>
  	<shape value="conical">
   	   <angle value="90" />
    	</shape>
	<primitive value="quad"/>
	<offset x="0" y="-0.9" z="0"/>
	<direction x="0.0" y="1" z="0"/>
	<color red="1" green="1" blue="1" alpha="1" />
	<color-no-energy red="0" green="0" blue="1" alpha="1" />
    	<radius value="0" />
    	<size value="0.1" />
    	<size-no-energy value="0.4" />
    	<speed value="2.0" />
	<speedUp constant="0" relative="-0.05"/>
	<gravity value="0"/>
    	<emission-rate value="0.5" />
    	<energy-max value="170" />
    	<energy-var value="0" />
	<relative value="true" />
    	<fixed value="true" />
    	<teamcolorNoEnergy value="false" />
    	<teamcolorEnergy value="false" />
</unit-particle-system>
```

The Crown
```Xml
<unit-particle-system>
    	<texture value="true" path="images/particle.bmp" luminance="true"/>
	<mode value="normal"/>
  	<shape value="conical">
   	   <angle value="90" />
    	</shape>
	<primitive value="quad"/>
	<offset x="0" y="0.9" z="0"/>
	<direction x="0.0" y="0.1" z="0"/>
	<color red="1" green="1" blue="1" alpha="1" />
	<color-no-energy red="0" green="0" blue="1" alpha="1" />
    	<radius value="0" />
    	<size value="0.2" />
    	<size-no-energy value="1" />
    	<speed value="2.0" />
	<speedUp constant="0" relative="-0.05"/>
	<gravity value="-0.05"/>
    	<emission-rate value="0.5" />
    	<energy-max value="230" />
    	<energy-var value="0" />
	<relative value="true" />
    	<fixed value="true" />
    	<teamcolorNoEnergy value="false" />
    	<teamcolorEnergy value="false" />
</unit-particle-system>
```