VeDbusItemImport: fix bug, it should always get signals

Problem:
VeDbusItemImport returns the cached value if someone calls
VeDbusItemImport.get_value(..)). Therefore code relies on being subscribed
to the PropertiesChanged signal. Without those signals coming in, get_value()
would forever return the initial value.

The code was trying to be clever, and only connected to the signals when a
callback function was passed to VeDbusItemImport.__init__(). All code that I
can think of does pass the callback, so this bug probably did not occur on
any of the CCGX projects.

Solution:
Took away the clever stuff, and moved the connect-to-signal() call to
__init__().

Also renamed dbus._object to dbus._proxy, that is a better name.
VeDbusItemImport: disabled introspects, reducing system load

And disabling the introspections also gets rids of all the error messages in
the log of vrmlogger and vrmpubnub during powerup:
ERROR:dbus.proxies:Introspect error on :1.4:/Yield/Yesterday: dbus.exceptions.DBusException: org.freedesktop.DBus.Error.UnknownObject:
ERROR:dbus.proxies:Introspect error on :1.4:/Equalization/TimeRemaining: dbus.exceptions.DBusException: org.freedesktop.DBus.Error.UnknownObject:
VeDbusItemImport.__init__(): do not call get_value() twice

It was called twice, first to see if the path exists, and then another
time to save the value. Causing unnecessary context switches.

Not any more!
fixed vedbus unittests
cleanup: removed unused files and fixed examples
Fixed memleak in VeDbusItemImport, and in dbusmonitor

All projects using dbusmonitor should upgrade to this version of velib_python.
VeDbusItemImport objects were not being released when a D-Bus service
dissapears from the D-Bus, because the Python garbage collector does not remove
objects with a cyclic reference that have a __del__() statement.

For details, see comments in vedbus.py -> VeDbusItemImport.

To reproduce the problem, run vrmlogger, vrmpubnub or just dbusmonitor.py, and
make a script that continuously publishes a service on the D-Bus and goes off-
line again after a few seconds. All this ofcourse with a version of
VeDbusItemImport that has a __del__() statement!