Fix "Gtk was imported without specifying a version first"

Fixes the following warnings:

    sys:1: PyGIWarning: Gtk was imported without specifying a version first. Use gi.require_version('Gtk', '3.0') before import to ensure that the right version gets loaded.
    sys:1: PyGIWarning: Notify was imported without specifying a version first. Use gi.require_version('Notify', '0.7') before import to ensure that the right version gets loaded.

lib/solaar/gtk.py

@@ -20,6 +20,8 @@
 
 from __future__ import absolute_import, division, print_function, unicode_literals
 
+import importlib
+
 
 from solaar import __version__, NAME
 import solaar.i18n as _i18n
@@ -31,7 +33,7 @@ import solaar.cli as _cli
 
 def _require(module, os_package):
 	try:
-		__import__(module)
+		return importlib.import_module(module)
 	except ImportError:
 		import sys
 		sys.exit("%s: missing required package '%s'" % (NAME, os_package))
@@ -85,7 +87,8 @@ def main():
 	if not args: return
 	if args.action: return _cli.run(args.action, args.hidraw_path)
 
-	_require('gi.repository', 'python-gi')
+	gi = _require('gi', 'python-gi')
+	gi.require_version('Gtk', '3.0')
 	_require('gi.repository.Gtk', 'gir1.2-gtk-3.0')
 
 	try:

lib/solaar/ui/notify.py

@@ -29,9 +29,17 @@ from solaar.i18n import _
 #
 
 try:
+	import gi
+	gi.require_version('Notify', '0.7')
 	# this import is allowed to fail, in which case the entire feature is unavailable
 	from gi.repository import Notify
 
+	# assumed to be working since the import succeeded
+	available = True
+except (ValueError, ImportError):
+	available = False
+
+if available:
 	from logging import getLogger, INFO as _INFO
 	_log = getLogger(__name__)
 	del getLogger
@@ -39,9 +47,6 @@ try:
 	from solaar import NAME
 	from . import icons as _icons
 
-	# assumed to be working since the import succeeded
-	available = True
-
 	# cache references to shown notifications here, so if another status comes
 	# while its notification is still visible we don't create another one
 	_notifications = {}
@@ -137,8 +142,7 @@ try:
 			except Exception:
 				_log.exception("showing %s", n)
 
-except ImportError:
-	available = False
+else:
 	init = lambda: False
 	uninit = lambda: None
 	# toggle = lambda action: False