[BUGFIX] Extend DataHandler override from TCEmain for compatibility

This change should allow the overrides to work on installs using hook processors which needlessly define a required class name on the fourth parameter of most TCEmain hook call dispatching functions.

Although this adds yet another class inheritance layer it's preferable to allowing unpatched third-party extensions such as TemplaVoila to fail.

Fixes: #22
Merge pull request #50 from NamelessCoder/issue/22

[BUGFIX] Extend DataHandler override from TCEmain for compatibility