WML: fix embedded Lua code & use new default styles

Summary:
In the previous diff of WML (D17891), I forgot to update the styles as mentioned by dhaumann in the comment (sorry!).

I also noticed that the Lua code is incorrectly highlighted, due to the incorporation of the Shebang in lua.xml (wml.xml is older). Searching, this is the only file with the inclusion of ##Lua.

Reviewers: Framework: Syntax Highlighting, dhaumann

Reviewed By: Framework: Syntax Highlighting, dhaumann

Subscribers: kwrite-devel, kde-frameworks-devel

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D17957