Speed-up PTC fringe fields

[ldeniau]

In file Sh_def_kind.f90, set the global-to-module variable
n_wedge = 0
instead of 5, this will save 5*(8+7)*2 = 150 yrotation done for each element

[ldeniau]

As a side comment, in some conditions, these yrotation are needed to get accurate results... So this needs to be investigated further, even if it slows down PTC.

[jgray-19]

This has been implemented as of #1200.