MA: MA 146 exit numbers

[froggie]

Given past precedent for changing to/using exit numbers for waypoints on state route freeways, is it worth converting additional points on the MA 146 list to the exit numbers?  I drove through yesterday and noticed these exit numbers signed at waypoints we're using the road name/route number for:

I-290  -->  13
MA122A_N  -->  12
MilSt  -->  11
I-90/20  -->  10
MA122A_S  -->  9

[yakra]

Done.
Also changed MA122AWor labels to conform.
https://github.com/TravelMapping/HighwayData/pull/698