Draft: WIP slap/slap.py: use the json rpc entry points

• add callJsonRpcAPI method
• Drop GET/POST methods

slap/hateoas:

• drop unwanted parameters and old compatibility
• reduce number of errors catched/rewriten by do_request

slap/exception:

• all slap Exception must have a common parent class This will allow to catch only the slap exceptions.

grid/slapgrid:

• drop not needed try/except
• WIP: desactivate offline support, as it catches too many errors
• reduce cases when slapgrid switch to offline mode
• slapgrid: desactivate handling of transaction file

test_slapgrid:

• return 404 instead of 500 if url is not handled

slap.py: use new entry points