Validity / Visibility should have an `inverse` attribute

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The Validity / Visibility xml element in Configuration Files should have an attribute to inverse the logic of the validity/visibility. For instance, inverse the fileextensions attribute.

A typical use case is the following:

• A split file menu accept only a single file. When executed, it generates multiple files of which the first "part" has the file extension 001.
• A join files menu accept all files that matches fileextensions="001"

Edit:
To prevent the split file menu to be displayed when user selects a *.001 file (we don't need to split a file twice), the menu should also not accept files that matches fileextensions="001".

In the end, the split file menu validity should be:

1. accept only a single file.
2. accept files which file extension is not 001.

The validity element should look like this:

<validity maxfiles="1" maxfolders="0" fileextensions="001" inverse="fileextensions" />

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More examples:

• <validity fileextensions="001" inverse="fileextensions" />, valid when the file is not a *.001 file.
• <validity maxfiles="1" maxfolders="0" inverse="maxfiles" />, valid when more than one file is selected.
• <validity properties="process.started" inverse="properties" />, valid when the property is not yet specified.
• <validity exists="${env.USERPROFILE}\config.ini" inverse="exists" />, valid only when the user's configuration file is not yet created.

The inverse attribute should be a list (separated with ; character) to allow insersing multiple attributes.

The attribute should allow the all value to inverse all attributes.

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Feature implemented in master branch in commit 455192c.