Remove tf subscription from frame manager and use tf buffer instead

[shrijitsingh99]

Summary:

1. Removes subscription of tf since buffer already does that internally
2. Since now there is no way to generate an event on an update of tf frames, therefore fetch the latest frames from the frame manager when and where it is needed and not rely on events to automatically update the frames.
3. Remove locks from functions that are mutually exclusive

[Sarath18]

Thank you for adding back the FrameListChanged event. Can you revert the changes in the AxesDisplay plugin and GlobalOptions plugin to update Combo-box on receiving the event? Everything else looks good.