BibIngest: new module to handle document ingestion

* Introduces a new module 'BibIngest' that handles document ingestion for
  Invenio. The module provides the basic CRUD functions: create, read, update
  and delete.

* Allows for multiple ingestion packages types and storage engines to be
  defined as plugins.

* A configuration file is provided where combinations of ingestion packages
  and storage engines can be defined per collection along with specific
  settings for each case.

Conflicts:
	configure.ac
	modules/Makefile.am
BibIngest: move module to legacy folder

Signed-off-by: Esteban J. G. Gabancho <egabancho@gmail.com>