New mixed triplet seed layers and updates to MVA selectors

[mhwalker]

This PR makes a small change to the mixed triplet seed layers to become consistent with the detached triplet seed layers and cuts.

There are also updates to improve the behavior of the MVA selectors. Changes were made to make the MVA calculated for each selector as opposed to for each iteration. We added pT as a variable to the MVA. Support for two sets of MVA variables was added. "Prompt" MVA includes d0 and dz infomation. "Detached" MVA does not, which is the same as the previous version. We also changed the way vertex matching is done: if a track has weight for a vertex, it is associated to that vertex; otherwise it is associated to the nearest in dz. A couple minor bug fixes were made as well.

This PR will have to accompany a new payload for the MVA.

The changes will be discussed in the TRK POG meeting on 18 May (sorry for the late notice).

[VinInn]

A first look to the comparison shows changes as expected: we are now removing many more 3-5 hits tracks in particular in the overlap region. High statistics relval are of course required.
I do not exclude some retuning once we get high-stat results and feed-back from other POGs/PAGs.
An igprof comparison would be useful as well.

[slava77]

+1

for #9119 870ce2c

• tested locally in CMSSW_7_5_X_2015-05-25-2300 /test area sign558/
• from the hcal pf calibration side: there is a small decrease in response (to balance the small increase that was brought in by the HCAL 25ns reco update  #9154
• for the tracking part the changes are in line with earlier presentations: fake rates go down, efficiency is about the same (plots are from 25202)

• there is also an indication of improvements in b-tagging