track parent in kernel

raw_input / getpass are not lambdas, but Kernel methods.
parent state is tracked in Kernel traitlets.
password key added to input_request
fix inprocess input request
handle getpass in terminal frontend
add utils.tokenutil for getting the token at a cursor offset
add object_inspect_text

in preparation for object_info_request returning formatted mime-bundle
update completion_ and objection_info_request

both requests take:

- code (full cell)
- column (cursor col)
- line (cursor line)

and object_info_replies return a mime-bundle, instead of structured data