adjust User test to recent changes

see #11
add further properties for Repositories
adding deep_const_ptr
Revert "adding deep_const_ptr"

This reverts commit 2c657e67aa292f6f6c1bd51b6f9f73828c0807cd.
add deep_const_ptr (and improved it)
using deep_const_ptr for q-pointers
add pull/push/remove functionality for Things

Though this requires the `Thing`s to hold a pointer to the global
Manager, it enables a more intuitive and flexible API.
The `Things` can now carry out their actions directly.
This enables further specialized API calls, e.g. get the followers of a
User, contributers of a Repo etc.
add test case for Thing::pull
docu for pull/push/remove functions

+ plus some basic error checking
some code cleanup
Merge branch 'global-manager'

Conflicts:
	src/ghapi/thing.cpp