Use GeoAlchemy2 instead of GeoAlchemy (Support for CKAN>=2.3 and PostGIS 2.x)

[amercader]

GeoAlchemy does not play well with the SQLAlchemy version that CKAN 2.3 uses, returning these errors:

  File "/usr/lib/ckan/local/lib/python2.7/site-packages/geoalchemy/__init__.py", line 2, in <module>
    from geoalchemy.base import *
  File "/usr/lib/ckan/local/lib/python2.7/site-packages/geoalchemy/base.py", line 242, in <module>
    class SpatialComparator(ColumnProperty.ColumnComparator):
AttributeError: type object 'ColumnProperty' has no attribute 'ColumnComparator'

It also does not support PostGIS 2.0, which is the default on Ubuntu 14.04 and what everybody should be using really.

Plan is to drop support for geoalchemy, add a check on the plugin startup to warn users to update and update the docs and tests.

[amercader]

We actually still need to support GeoAlchemy for CKAN < 2.3 users.

So, to sum up:

CKAN	SQLAlchemy	GeoAlchemy	Supports PostGIS 1.5	Supports PostGIS 2.0
2.2	0.7.9	1	✅	❌ (?)
2.3	0.9.6	2	✅	✅