better function names; pointer tweaks

* OAuth token validation methods now two distinct forms
  - has* as const methods
  - verify* as non-const methods calling GitHub
* lastResponse is now handeled as shared pointer
* adjusted tests accordingly
tweaking and cleaning up debug output
only count HTTP status codes smaller 400 as errors
update docu for Manager; cleanup OAuth token verification API
basic layout for out-of-source documentation
tweak Doxygen output
update docu for AuthInfo
update and extend docu for INetwork and Network
further tweaks to Doxygen output
extending documentation