Update the chord parameter packing in  in main_wing_planform

update naming to Wing.chords.root and Wing.chords.tip
Apply PEP8 formatting for wing planform files - not sure if these really conform to coding style.
Renamed chord_mid to chord_mid_trap to reflect trapezoidal wing. 
this variable name doesn't look like it's in the data structure.  check this page out --

https://docs.google.com/document/d/1L_T05NWoyAKlwvofUGF6MZHFxmtGtLuSxU-w5v3l2C8/edit#heading=h.3soqcnwn495f

it should be somewhere along the lines of ```Wing.chords.mean_geometric```.  if this method is calculating a different chord, we need to sort this out as a group, since this quantity is used in a couple places