Improved Emacs mode line detection

[peter-b]

In a file opened with Emacs, having -*-Makefile-*- in the first line of the file will select Makefile editing mode. There's no need to have a mode: specifier, so it would be nice not to have to include mode: in language-livecode's detection regexp.

Also, we don't currently have any options for how to specify LiveCode Builder vs LiveCode Script mode.

What about case-insensitively using -*-livecode-*- or -*-livecode[script]-*- for LCS mode, -*-livecode[server]-*- for LiveCode Server / revIgniter mode, and -*-livecode[builder]-*- for LCB mode?