DiagramGrid._merge_premises_conclusions: Use itertools.chain.
DiagramGrid._merge_premises_conclusions: Use itertools.chain.

This simplifies the method and outsources the functionality to better
functions.

jbbskinny/sympy,toolforger/sympy,grevutiu-gabriel/sympy,kmacinnis/sympy,skidzo/sympy,Sumith1896/sympy,Gadal/sympy,liangjiaxing/sympy,oliverlee/sympy,kaushik94/sympy,amitjamadagni/sympy,jerli/sympy,jbbskinny/sympy,mcdaniel67/sympy,toolforger/sympy,Vishluck/sympy,Vishluck/sympy,farhaanbukhsh/sympy,ChristinaZografou/sympy,abhiii5459/sympy,dqnykamp/sympy,lidavidm/sympy,Sumith1896/sympy,lindsayad/sympy,madan96/sympy,kaushik94/sympy,sahilshekhawat/sympy,madan96/sympy,AunShiLord/sympy,MechCoder/sympy,postvakje/sympy,debugger22/sympy,kumarkrishna/sympy,Gadal/sympy,kumarkrishna/sympy,skirpichev/omg,moble/sympy,Designist/sympy,abloomston/sympy,sampadsaha5/sympy,iamutkarshtiwari/sympy,jamesblunt/sympy,shipci/sympy,mcdaniel67/sympy,AkademieOlympia/sympy,cccfran/sympy,garvitr/sympy,asm666/sympy,Designist/sympy,wanglongqi/sympy,hargup/sympy,aktech/sympy,jbbskinny/sympy,skidzo/sympy,saurabhjn76/sympy,MridulS/sympy,dqnykamp/sympy,cccfran/sympy,kevalds51/sympy,iamutkarshtiwari/sympy,sahilshekhawat/sympy,saurabhjn76/sympy,flacjacket/sympy,jamesblunt/sympy,rahuldan/sympy,Curious72/sympy,jamesblunt/sympy,AkademieOlympia/sympy,MridulS/sympy,shipci/sympy,yashsharan/sympy,drufat/sympy,ChristinaZografou/sympy,yukoba/sympy,Shaswat27/sympy,Vishluck/sympy,abhiii5459/sympy,Mitchkoens/sympy,souravsingh/sympy,Davidjohnwilson/sympy,Gadal/sympy,atreyv/sympy,yukoba/sympy,souravsingh/sympy,rahuldan/sympy,sunny94/temp,kevalds51/sympy,sunny94/temp,chaffra/sympy,pandeyadarsh/sympy,drufat/sympy,bukzor/sympy,aktech/sympy,vipulroxx/sympy,lindsayad/sympy,rahuldan/sympy,ga7g08/sympy,oliverlee/sympy,pandeyadarsh/sympy,jaimahajan1997/sympy,dqnykamp/sympy,kevalds51/sympy,VaibhavAgarwalVA/sympy,sunny94/temp,jaimahajan1997/sympy,MechCoder/sympy,moble/sympy,shikil/sympy,hargup/sympy,VaibhavAgarwalVA/sympy,toolforger/sympy,atsao72/sympy,yashsharan/sympy,wanglongqi/sympy,Arafatk/sympy,souravsingh/sympy,Mitchkoens/sympy,chaffra/sympy,grevutiu-gabriel/sympy,MechCoder/sympy,AunShiLord/sympy,atsao72/sympy,cswiercz/sympy,vipulroxx/sympy,kaichogami/sympy,abhiii5459/sympy,jerli/sympy,Titan-C/sympy,hrashk/sympy,Mitchkoens/sympy,farhaanbukhsh/sympy,beni55/sympy,hrashk/sympy,emon10005/sympy,Shaswat27/sympy,emon10005/sympy,kaichogami/sympy,sampadsaha5/sympy,pbrady/sympy,Sumith1896/sympy,mafiya69/sympy,pbrady/sympy,asm666/sympy,liangjiaxing/sympy,cswiercz/sympy,maniteja123/sympy,AkademieOlympia/sympy,debugger22/sympy,kmacinnis/sympy,jerli/sympy,pbrady/sympy,abloomston/sympy,MridulS/sympy,debugger22/sympy,AunShiLord/sympy,Davidjohnwilson/sympy,mafiya69/sympy,sahmed95/sympy,atreyv/sympy,pandeyadarsh/sympy,hrashk/sympy,amitjamadagni/sympy,Curious72/sympy,beni55/sympy,Shaswat27/sympy,madan96/sympy,asm666/sympy,wyom/sympy,wyom/sympy,mcdaniel67/sympy,sahilshekhawat/sympy,yashsharan/sympy,ChristinaZografou/sympy,wyom/sympy,diofant/diofant,cswiercz/sympy,maniteja123/sympy,sampadsaha5/sympy,Arafatk/sympy,ahhda/sympy,Davidjohnwilson/sympy,meghana1995/sympy,postvakje/sympy,chaffra/sympy,mafiya69/sympy,beni55/sympy,shipci/sympy,atsao72/sympy,drufat/sympy,lidavidm/sympy,Arafatk/sympy,cccfran/sympy,garvitr/sympy,ga7g08/sympy,jaimahajan1997/sympy,oliverlee/sympy,postvakje/sympy,meghana1995/sympy,liangjiaxing/sympy,VaibhavAgarwalVA/sympy,lidavidm/sympy,kumarkrishna/sympy,Designist/sympy,iamutkarshtiwari/sympy,yukoba/sympy,meghana1995/sympy,grevutiu-gabriel/sympy,ahhda/sympy,farhaanbukhsh/sympy,skidzo/sympy,maniteja123/sympy,ahhda/sympy,kaushik94/sympy,abloomston/sympy,shikil/sympy,hargup/sympy,bukzor/sympy,shikil/sympy,srjoglekar246/sympy,kaichogami/sympy,ga7g08/sympy,Titan-C/sympy,saurabhjn76/sympy,wanglongqi/sympy,Curious72/sympy,Titan-C/sympy,moble/sympy,atreyv/sympy,lindsayad/sympy,emon10005/sympy,vipulroxx/sympy,aktech/sympy,sahmed95/sympy,sahmed95/sympy,garvitr/sympy,kmacinnis/sympy,bukzor/sympy