sTGC offline DQ: fix strip eff code

• Add a loop over large and small sector.
• Moving the definition of sTGCeff effPlots matrix bellow !meTrack conditional
• This is to ensure that only one muon track is verified for each sector, multiplet and layer.

I opened this MR following comments that @chchau and @gvasquez gave me:

""" The local coordinates are calculated with respect to the center of the surface. So you can get the radius to the center of the surface:

Get the global position of the 1st strip and last strip compute the radius to the center of the chamber: radius_position_1st_strip + (radius_position_last_strip - radius_position_1st_strip) / 2 then you can simply add it to the local x-position of the strip

Alternatively, you can replace the efficiency vs r with the efficiency vs strip number """

I would like to open the discussion here in order to have good feedback :).

Tagging @carquin @gvasquez @chchau @pscholer @jojungge