create a caching module using dogpile.cache

this module provides convenience functions to init/get/invalidate
dogpile.cache regions
setup everything so that caching is ready in the pyramid app
actually cache themes and internal WFSTypes

and some refactoring

Note that errors handling should be refactored, so that errors
can be cached with the _themes method which is already cached
refactor _getVars method
refactor error handling

so that errors are also cached with related _themes method

this commit also addresses issue #363
add cache invalidation strategy

cache will be invalidated when pyramid app is (re)started
and when appropriate db models are inserted/updated/deleted
fix tests that fail because of missing cache
fix functional tests that fail because of missing cache
update CONST_CHANGELOG.txt_tmpl with migration instructions related to caching
also cache the wms getcap response and remove role_id from the getcap requests

(role_id is removed from both wms/wfs getcap requests)
add dogpile versions in buildout.cfg [versions] section
update the dogpile.cache configuration instructions
consistency
update mapfile administrator doc to warn that apache has to be reloaded
Merge pull request #351 from bbinet/dogpile_cache

c2cgeoportal caching system
Update devlopper buildout file
Typo
Better extent (initial mapfile)
Use srid 21781 not -1
Enable WFS for default layer config