Use QWebEngineView for Manual Panel

The TaurusMainWindow "Manual" Panel uses the deprecated
QtWebkit.QWebView widget for displaying the manual, which
is not directly available from PyQt5 or PySide.

Replace it by its successor QtWebEngineWidgets.QWebEngineView

Closes taurus-org#1163

lib/taurus/qt/qtgui/container/taurusmainwindow.py

@@ -34,7 +34,7 @@
 
 from taurus import tauruscustomsettings, Release
 from taurus.core.util.log import deprecation_decorator
-from taurus.external.qt import Qt, compat
+from taurus.external.qt import Qt, compat, QtWebEngineWidgets
 from .taurusbasecontainer import TaurusBaseContainer
 
 from taurus.qt.qtcore.configuration import BaseConfigurableClass
@@ -1114,22 +1114,8 @@ def getQtDesignerPluginInfo(cls):
     def setHelpManualURI(self, uri):
         self.__helpManualURI = uri
         if self.helpManualBrowser is None:
-            try:
-                from taurus.external.qt.QtWebKit import QWebView
-
-                self.helpManualBrowser = QWebView()
-            except Exception:
-                self.helpManualBrowser = Qt.QLabel("QWebkit is not available")
-
-                def dummyload(*args):
-                    pass
-
-                self.helpManualBrowser.load = dummyload
-                return
-        try:
-            url = Qt.QUrl.fromUserInput(uri)
-        except Exception:
-            url = Qt.QUrl(uri)  # fallback for Qt<4.6
+            self.helpManualBrowser = QtWebEngineWidgets.QWebEngineView()
+        url = Qt.QUrl.fromUserInput(uri)
         self.helpManualBrowser.load(url)
 
     def getHelpManualURI(self):