Fix class name in a comment

(cherry picked from commit fc7ad8ec85ac3cd6fb9596e3eedeac370ff78c79)
WICKET-4703 StringResourceModel should provide an overridable getString(Component) method

Make StringResourceModel#getString(Component) overridable

(cherry picked from commit 1a5551273396d3babb79146b23e4d3afd42da3e8)