added grids command

--HG--
branch : util_grids
added tool to display configured grids. Only works with a valid MapProxy configuration file

--HG--
branch : util_grids
added test config for mapproxy-util grids tool

--HG--
branch : util_grids
added testclass for mapproxy-util grids tool

--HG--
branch : util_grids
test that fwd_req_params will be forwarded to outgoing getmap requests
add dimension_params property to MapQuery class
add method "update" to class NoCaseMultiDict and RequestParams
forward fwd_req_params to outgoing getmap requests
test that fwd_req_params will also work for combined sources
make fwd_req_params also work for combined sources
add documentation for 'forward-req-params'
hg merge
typo in doc
refactored mapproxy-util grids command

--HG--
branch : util_grids
forward mapproxy current os.environ when spawning a mapserver process
refactored MapQuery.dimensions
update documentation for forward_req_params
merge in changes from 1.4.x
update AUTHORS.txt
merge with 1.4.x