Start to share SWIG interface files between languages.

Summary:
Move scripts/Python/interface to scripts/interface so that we
can start making iterative improvements towards sharing the
interface files between multiple languages (each of which would
have their own directory as now).

Test Plan: Build and see.

Reviewers: zturner, emaste, clayborg

Reviewed By: clayborg

Subscribers: mjsabby, lldb-commits

Differential Revision: http://reviews.llvm.org/D9212

llvm-svn: 235676