Implemented BaseQuery.request() with caching
Do not cache QueryWithLogin.login()
Updated login() of Ukidss
Eso package upgrade

Use baseQuery.request()
Use StringIO, BytesIO from io package
Fixes for python2.6: “{0}”.format()
Do not cache data_retrieval(), save fits files in cache
Added get_header() to Eso package.
Setup eso tests package.
Updated Eso tests, removing @remote_data
Turned Eso tests into a package.
Added data cache for Eso tests.
Merge pull request #289 from jwoillez/issue287

An attempt to deal with issue #287, applied to the eso package.