Extension of mission definition for (instantaneous) configuration changes

[ErwinMoerland]

the <../missionDefinition> should be extended with instantaneous changes in payload and for in-air refuelling

The idea is to add nodes to the part within a definition, such that in-air refuelling and payload changes can be explicitly defined during a segment.

• current implementation: as endCondition of a segment. This is not preferred (from a teleconference concerning connection of flight dynamics considerations within the Diabolo project):

<missionDefinitions>
  <segments>
    <segment>
      <endCondition>
          <releasedStores>
            <releasedStore>
              <uID>
              <quantity>

• suggested implementation (to be worked out in more detail):

<missionDefinitions>
  <segments>
    <segment>
      <constraints>
        <constraint>
          <referenceEndCondition>
          <endConditionRatio>
          <inAirRefueling>
          <releaseStores>