perf($resource): use shallow copy instead of angular.copy
perf($resource): use shallow copy instead of angular.copy

Replace calls to angular.copy with calls to a new function, shallowClearAndCopy.
Add calls to copy for cache access in $http in order to prevent modification of cached data.
Results in a measurable improvement to the startup time of complex apps within Google.

Closes #5300

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js