#271 deprecate taurus.external.ordereddict

[Carlos Pascual]

Taurus does not use taurus.external.ordereddict (sardana does, though).
Also, OrderedDict is provided by the collections module since Python2.7 and by the orderedict package (available from pypi) for earlier python versions, so we should remove it (previous deprecation) and suggest those using it to require either Python>=2.7 or ordereddict

[Carlos Pascual]

As a first step to fix this, I created a PR for deprecating it in taurus 4.0 https://github.com/cpascual/taurus/pull/29

The idea is to effectively remove it for the Jan17 release