refine json loading process

- now dynamic load validation modules for in a new function:
SwaggerApp.validate
- SwaggerApp._create_ is now splitted into several functions: validate,
load, prepare
replace JsonPath with JsonPointer

what Swagger officially used.
fix TypeReducer
replace scope, name with JsonPointer
remove Resolver and Fixer
an obvious bug, should be list
make a copy of default value

if not, all properties would reference to the same object.
make a copy for default value
make sure we use json-pointer to represent path
return dict instead of list from BaseObj._children_
fix bug

a tuple, not 2 variables.
move spec invariant testing script out of v1_2