Properly serialize data into request body instead of url.

Closes #887

this was never meant to be a public api used by apps. I refactored
the code to hide the functionality.

BREAKING CHANGE: $browser.addJs method was removed

apps that depended on this functionality should either use many of the
existing script loaders or create a simple helper method specific to the
app.

Breaks angular.fromJson which doesn't deserialize date strings into date objects.

This was done to make fromJson compatible with JSON.parse.

If you do require the old behavior - if at all neeeded then because of
json deserialization of XHR responses - then please create a custom
$http transform:

$httpProvider.defaults.transformResponse.push(function(data) {
  // recursively parse dates from data object here
  // see code removed in this diff for hints
});

Closes #202