massBreakdown: linking geometry

[MarAlder]

There is no connection between the mass definition in the massBreakdown and the corresponding geometric descriptions. This causes problems for sequence elements (e.g., which of the [1..inf] wing elements in wingsType corresponds to which of the [0..inf] mWingStructure elements in mWingsStructureType):

<wings>
    <wing uID="myFavoriteWing">...</wing>
    <wing uID="anotherWing">...</wing>
    <wing uID="aLittleWing">...</wing>
</wings>

and

<mWingsStructure>
    <massDescription>...</massDescription>
    <mWingStructure>
         <massDescription>
             <!-- Description: UID of the component which serves as parent element, i.e. whose coordinate system is to be used as a reference for the mass properties (CoG location, orientation and massInertia). Thus, two cases can occur: (1) it is set: local coordinate system of the parent; (2) it is not set: global CPACS coordinate system. " -->
             <parentUID>...</parentUID>
             <!-- PROPOSAL: -->
             <!-- Description: UID of the component which contains more detailed information, e.g. on geometric dimensions. It does not influence the coordinate systems definition. -->
             <geometryUID>myFavoriteWing</geometryUID>
         </massDescription>
    </mWingStructure>
</mWingsStructure>

Or another example with systems:

We could add something like a geometryUID element to genericMassType to enrich the massBreakdown with geometry information if available. It would then of course also apply for mass breakdown elements for which a goemetry is not avaiable in CPACS, but it is an optional element.

[MarAlder]

Renamed to componentUID and implemented (006becae). Needs review.