Removed kschur.py
remove import kschur from classical.py and inaccessible if statements
remove stray import statement from algebras/nil_coxeter_algebra.py
Merge branch 'public/combinat/sf/fixes-15575' of trac.sagemath.org:sage into 15575
salvaging the doc from kschur.py
correcting my own errors
removing a bad idea I blindly copied from the old docstrings
additions to documentation
fixes to new_kschur documentation
clarification on meaning of lift
Trac #15575: Remove deprecated functions from symmetric functions

The class for each basis of the symmetric functions was deprecated from
the global name space in #5457 and the ticket was merged in sage-5.4.

The this ticket will remove the following functions:

 `kschur.py`

The way of accessing these functions since sage-5.4 is to get the basis
from within `SymmetricFunctions(R)`.

URL: http://trac.sagemath.org/15575
Reported by: zabrocki
Ticket author(s): Anne Schilling, Mike Zabrocki
Reviewer(s): Travis Scrimshaw