Lazy Commands/DataRefs.txt loading breaks upgrading of resources for existing projects

[tngreene]

1. Make a .blend file,
2. Toggle the search window, that resource will load and be saved in command_search_window_state or dataref_search_window_state
3. Save and close
4. Replace those resources
5. Open .blend back up
6. Since these state variables already have content, they wont get refreshed.

I see two options:

1. load_handler clears both the state variable and the module's private global variable
   2.. We get rid of lazy loading

I vote 2 because it is more trouble than it is worth (with such a small amount of lines of text).

[tngreene]

If you are stuck, execute this in an interpreter window and attempt to use the feature again:

import io_xplane2blender
import bpy
io_xplane2blender.xplane_utils.xplane_datarefs_txt_parser._datarefs_txt_content.clear()
bpy.context.scene.xplane.dataref_search_window_state.dataref_search_list.clear()

It doesn't touch important data.