fix(injector): allow multiple loading of function modules

Change HashMap to give $$hashKey also for functions so it will be possible to load multiple module
function instances. In order to prevent problem in angular's test suite,  added an option to HashMap
to maintain its own id counter and added cleanup of $$hashKey from all module functions after each
test.

Before this CL, functions were added to the HashMap via toString(), which could potentially return
the same value for different actual instances of a function. This corrects this behaviour by
ensuring that functions are mapped with hashKeys, and ensuring that hashKeys are removed from
functions and objects at the end of tests.

In addition to these changes, the injector uses its own set of UIDs in order to prevent confusingly
breaking tests which expect scopes or ng-repeated items to have specific hash keys.

Closes #7255