convert to utf8

I don't know if and what tests the maintainers would like... so setting to needs review.

@spuky
Required is:

• Config schema for the settings.
• A unit test for the tampering part of the plugin. In this case it should check if the configured encoding is happening.
• A functional test for the configuration form of the plugin.

In the code I see that a submitConfigurationForm() method is missing. This causes that the configuration is not guaranteed to get saved (depends on the module using the Tamper plugin).

thanks that helps will provide them as time permits...