Camel casing that is better backward compatible with scrooge 3.0.3.

This patch changes the way camel casing is created. The goal of the change is
to be more compatible with Scrooge 3.0.3. In particular words like `HTML_REPORT`
are now again converted to `HtmlReport` in the Scala output.

Note that the change is also quite compatible with other spellings as none of
the tests (except for one detailed unit test) needed to be changed.