If the dbus server cannot be started or is not available, calling a notification
would result in an exception. During initialization check that we can get the
server information, and disable notifications if this is not possible.
Note: we change dnotify.d from the originally distributed version to include
a check for availability function.
* add external sources for (d)notify with README and license statements
* add new logAndNotify function, make building a compile time option
* use logAndNotify and main.d, make timeout message silent
* update documentation for notification support
* add command line switch --disable-notifications
* add build-deps for libnotify in README.md
