[Refactor] C++11 Memory access iterators in SCoP stmts

+ Added const iterator version
+ Changed name to begin/end to allow range loops
+ Changed call sites to range loops
+ Changed typename to (const_)iterator


git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@210927 91177308-0d34-0410-b5e6-96231b3b80d8