Implemented _validate method in sequence classes
Implemented _validate method in sequence classes

Other small changes:
* Got rid of _foo properties
(https://github.com/sympy/sympy/pull/9435#discussion_r31267208)
* Other minor changes (Typo and such)

cswiercz/sympy,Vishluck/sympy,lindsayad/sympy,Arafatk/sympy,Curious72/sympy,Curious72/sympy,abhiii5459/sympy,maniteja123/sympy,shikil/sympy,maniteja123/sympy,garvitr/sympy,maniteja123/sympy,garvitr/sympy,debugger22/sympy,farhaanbukhsh/sympy,abhiii5459/sympy,yukoba/sympy,Shaswat27/sympy,abloomston/sympy,grevutiu-gabriel/sympy,Arafatk/sympy,sahmed95/sympy,atsao72/sympy,ahhda/sympy,wanglongqi/sympy,Designist/sympy,wyom/sympy,mafiya69/sympy,pandeyadarsh/sympy,jerli/sympy,oliverlee/sympy,madan96/sympy,rahuldan/sympy,moble/sympy,hargup/sympy,toolforger/sympy,Gadal/sympy,jaimahajan1997/sympy,bukzor/sympy,Davidjohnwilson/sympy,MechCoder/sympy,shikil/sympy,iamutkarshtiwari/sympy,jbbskinny/sympy,emon10005/sympy,MechCoder/sympy,souravsingh/sympy,bukzor/sympy,wyom/sympy,MechCoder/sympy,ChristinaZografou/sympy,kaichogami/sympy,sampadsaha5/sympy,ga7g08/sympy,mafiya69/sympy,atreyv/sympy,Designist/sympy,sampadsaha5/sympy,kaichogami/sympy,grevutiu-gabriel/sympy,cswiercz/sympy,VaibhavAgarwalVA/sympy,kevalds51/sympy,sahmed95/sympy,postvakje/sympy,debugger22/sympy,jerli/sympy,jaimahajan1997/sympy,kumarkrishna/sympy,skidzo/sympy,Shaswat27/sympy,pandeyadarsh/sympy,Shaswat27/sympy,mcdaniel67/sympy,VaibhavAgarwalVA/sympy,postvakje/sympy,toolforger/sympy,grevutiu-gabriel/sympy,yashsharan/sympy,rahuldan/sympy,chaffra/sympy,Arafatk/sympy,yukoba/sympy,Gadal/sympy,drufat/sympy,Vishluck/sympy,souravsingh/sympy,Davidjohnwilson/sympy,yashsharan/sympy,asm666/sympy,Designist/sympy,atsao72/sympy,farhaanbukhsh/sympy,debugger22/sympy,ga7g08/sympy,jerli/sympy,kaushik94/sympy,aktech/sympy,drufat/sympy,souravsingh/sympy,Curious72/sympy,chaffra/sympy,moble/sympy,hargup/sympy,oliverlee/sympy,saurabhjn76/sympy,yashsharan/sympy,kumarkrishna/sympy,ChristinaZografou/sympy,jbbskinny/sympy,bukzor/sympy,madan96/sympy,shikil/sympy,atsao72/sympy,lindsayad/sympy,kaushik94/sympy,wanglongqi/sympy,skidzo/sympy,kumarkrishna/sympy,lindsayad/sympy,ahhda/sympy,kevalds51/sympy,postvakje/sympy,mcdaniel67/sympy,rahuldan/sympy,sahmed95/sympy,abloomston/sympy,yukoba/sympy,atreyv/sympy,sampadsaha5/sympy,moble/sympy,skidzo/sympy,iamutkarshtiwari/sympy,saurabhjn76/sympy,kevalds51/sympy,asm666/sympy,chaffra/sympy,kaichogami/sympy,atreyv/sympy,oliverlee/sympy,emon10005/sympy,aktech/sympy,mafiya69/sympy,abhiii5459/sympy,jbbskinny/sympy,mcdaniel67/sympy,AkademieOlympia/sympy,Gadal/sympy,wanglongqi/sympy,garvitr/sympy,abloomston/sympy,jaimahajan1997/sympy,madan96/sympy,AkademieOlympia/sympy,kaushik94/sympy,saurabhjn76/sympy,emon10005/sympy,ga7g08/sympy,Titan-C/sympy,ChristinaZografou/sympy,pandeyadarsh/sympy,wyom/sympy,Titan-C/sympy,toolforger/sympy,farhaanbukhsh/sympy,cswiercz/sympy,AkademieOlympia/sympy,hargup/sympy,aktech/sympy,iamutkarshtiwari/sympy,drufat/sympy,Vishluck/sympy,ahhda/sympy,Titan-C/sympy,Davidjohnwilson/sympy,VaibhavAgarwalVA/sympy,asm666/sympy