Add (request|response)_cookie_t typedefs to make easier to read compiler error, when ContextT chain does not include cookie_context
Added webpp-common subproject
Created CommonLibs variable to simplify CMakeLists.txt
stacked exceptions: informative backtraces, with added per function informations (eg string processed when exception occured)
Basic documentation for cookie and encrypted cookie contextes.
Created missing function delete_cookie()