add `blade_%s:` prefix to geometry variables

[fzahle]

The blade planform is defined with the following parameters: ['x', 'y', 'z', 'rot_x', 'rot_y', 'rot_z', 'chord', 'rthick', 'p_le']. In the old OpenMDAO they were nested inside a vartree, making it clear that all these parameters belonged to a planform definition. Now that vartrees no longer exist, the first version we did simply had the parameters added and promoted with the above names. While names like chord are self-explanatory x y z are not. so to be more unambiguous I propose that we start using prefixes for these parameters, so they're referred to as e.g. blade_ae:s and blade_ae:chord. The pf parameters discretized for the structural calculations will then be named blade_st:s and blade_st:chord.

Any objections? @mrosemeier what do you think?

[mrosemeier]

I have no objections using prefixes. Would that more or less replace the suffixes that are currently added in the components, i.e. suffix='_st'?

[fzahle]

yes, the suffix in the current version will be become part of the prefix.

[fzahle]

FYI @tlbl and @pilotmm let me know if you have any comments.

And I won't merge this until we have adapted the other wrappers.

[pilotmm]

I think that change makes a lot of sense...