v01-15

2017-11-10 Ete Remi (PR#24)
- EventSelector inherits from EventModifier and call processEvent() from modifyEvent()
- Added safety clear of conditions in ProcessorMgr::modifyEvent
2017-11-10 Ete Remi (PR#23)
- Added constants replacement for condition attributes in the execute section
  - Allows permanent conditions at runtime (not depending on processor return values)
  - Allows to refer to constants in conditions in the execute section, e.g :
```
<constants>
  <constant name="RunOverlay" value="false" />
</constants>

<execute>
  <if condition="${RunOverlay}">
    <processor name="MyOverlayBg"/>
  </if>
</execute>
```
and run :
```
Marlin steering.xml --constant.RunOverlay=true
```
to change the behavior.

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