Fixed sorting, searching, and make M2M optional

import from gettext from flask.ext.admin.babel

in examples: import flask-sqlalchemy from flask.ext hook

in examples: import flask-sqlalchemy from flask.ext hook to support flask-SQLAlchemy>=0.16 (this change is also backwards compatible for <= 0.16)

PK for models is optional. Some model backends might not have PK and still will work with individuals records.