Added new function downloadMARCOAI(). Updated documentation.

downloadAlephDocument() renamed to downloadMARCXML().

downloadMARCOAI() will be used to query Aleph to track document progress
thru library acquisition process.

Removed list of VALID_ALEPH_BASES, which are very specific to each library
and 90% of them is virtual and they are dynamically added/removed by
librarians.
Other files adjusted to reflect changes in aleph.py.
Two classes changet do namedtuples.
test_convertors.txt moved from test_search.txt.

It makes sense to move it there, because it is standalone module.
Tests for configuration updated.