hellopane.py crashes when right-clicked

Version and Platform (required):

• Binary Ninja Version: 4.3.7046-dev
• OS: all
• OS Version: all
• CPU Architecture: all

Bug Description:
python/examples/hellopane.py does not actually initialize self.m_contextMenuManager or self.m_menu and so if you right-click on the pane itself, you get:

[ScriptingProvider] Traceback (most recent call last):
[ScriptingProvider]   File "C:\Users\joshwatson\AppData\Roaming\Binary Ninja\plugins\pane.py", line 112, in contextMenuEvent
[ScriptingProvider]     self.m_contextMenuManager.show(self.m_menu, self.actionHandler)
[ScriptingProvider]     ^^^^^^^^^^^^^^^^^^^^^^^^^
[ScriptingProvider] AttributeError: 'HelloPaneWidget' object has no attribute 'm_contextMenuManager'

Steps To Reproduce:
Please provide all steps required to reproduce the behavior:

1. Install python\examples\hellopane.py in the Binary Ninja plugins directory
2. Open the Hello Pane from the Plugins menu
3. Right-click the Hello Pane

Expected Behavior:
A context menu or something should probably show, but at least it shouldn't throw an exception

Start with python/examples/hellopane.py, especially HelloPaneWidget and its contextMenuEvent method, and compare how the context-menu members are set up before the right-click path runs. Reproduce the issue by opening the Hello Pane and right-clicking it; done means the action no longer raises the reported AttributeError and the intended context-menu behavior is defined.