Add optional hidden entries filter

[MortuusEquusPhobia]

Hi Markus,

Thank you for creating and maintaining SystemTrayMenu.

While using the application, I noticed that Windows system files such as 'desktop.ini'
and 'Thumbs.db' can appear in the menus. This pull request adds an
optional Hidden entries filter to the Expert page.

The filter:

• is empty by default, preserving the existing behavior
• supports multiple patterns separated by '|'
• supports '*' and '?' wildcards
• applies to both files and directories
• is cleared by the existing Default button

Example:

'desktop.ini|Thumbs.db|.bak|.tmp|.git'

I have tested the feature both with existing saved settings and from a
clean first-run configuration.

Thank you for your time.