u2py refactoring and improvements

+ It is no longer required to import lib from interface, since
interface_basis.load
now implicitly carries u2 library handle. All dependant modules have
been updated
to reflect this change.
+ ByteArray moved from u2py.interface to u2py.interface_basis.
It also got doctest to prevent possible regressions.
All dependant modules have been updated to reflect this change.
+ u2py.interface.Reader split into 2 inheritance-linked parts:
u2py.interface_basis.BaseReader and u2py.interface.Reader
to make possible usage of Reader without importing NFC cards facilities.
+ u2pt.interface_basis and u2py.interface got ctypes.addressof replaced
by ctypes.byref.
+ u2py.contract:
* now using byref instead of addressof;
* DYNAMIC_A got context handling methods for future usage;
* DYNAMIC_A.commit now looks better.
+ u2py.card_event, u2py.contract, u2py.db, u2py.term no longer directly
depend on u2py.interface.
+ All aforementioned changes have been tested with internal test suite
using FileImpl.
Version 1.6.10

+ u2py.contract got some docs clarifications.
+ u2py.staff.CONTRACT0_DYNAMIC should now properly interact with CONTRACT_A facilities:
  * added update_checksum method;
  * added comparison operator to correctly detect earliest version of dynamic data.