Scene.py add _hideReloadMessage, connect to startReloadAll

[dfries]

When all files are being reloaded, the file modification reload dialog is redundant. This allows pressing F5 to reload and dismiss the dialog.

Description

This commit depends on the Cura commit "Add startReloadAll signal when reloadAll is called" in pull request Ultimaker/Cura#19608, which adds the signal startReloadAll. This Uranium change will connect to the signal to cancel file modification reload dialog. Once all the models
are reloaded, the file modification reload dialog is not needed.

Type of change

• New feature (non-breaking change which adds functionality) I could argue this is a bug.

How Has This Been Tested?

• Exercise F5 reloadAll

1. Load a set of models
2. Externally modify a file
3. Verify "File has been modified" dialog shows, don't click it
4. Press F5, verify the new model shows and "File has been modified" dialog hides

Test Configuration:

• Operating System: Debian Linux

Checklist:

• My code follows the style guidelines of this project as described in UltiMaker Meta and Cura QML best practices
• I have read the Contribution guide
• I have commented my code, particularly in hard-to-understand areas
• I have uploaded any files required to test this change