[TxMt] Add a new enging for LaTeX Bundle

[Marco Daniel]

Hi,

TeXMate have the following engines predefined:
- pdflatex
- latex
- xelatex
- texexec

However I want to add some new default engines e.g. lualatex, arara, 
luatex, pdftex.

I know that I can work with %!TS-program = luatex but this isn't what I 
want to achieve.

How can I add a new default engine.

Thanks for your help
Marco Daniel