moved src/stan/math/error_handling to src/stan/error_handling
moving all files in error_handling to error_handling/scalar
moved namespaces from math to error_handling
changed the test names to reflect different namespaces
switching namespaces for error_handling
Merge branch 'develop' into feature/issue-1102-move-error_handling

Conflicts:
	src/stan/prob/distributions/univariate/discrete/poisson.hpp
Merge pull request #1107 from stan-dev/feature/issue-1102-move-error_handling

Fixes #1102. Move error_handling