Fix include/editor order in mc.ext

[legends2k]

mc.ext has

` shell/i/.tex

Include=editor`

However, include/editor, where the Open action calls $EDITOR, is defined above this; hence .tex files aren't opened on Enter key press.

Moving include/editor below all Include=editor occurrences fixes this. I've given the patch for this too.

Additionally, I took the liberty to associate Markdown files in mc.ext.

Build Details
GNU Midnight Commander 4.8.22
Built with GLib 2.58.2
Using the S-Lang library with terminfo database
With builtin Editor
With subshell support as default
With support for background operations
With mouse support on xterm
With internationalization support
With multiple codepages support
Virtual File Systems: cpiofs, tarfs, sfs, extfs, ftpfs, sftpfs, fish
Data types: char: 8; int: 32; long: 64; void *: 64; size_t: 64; off_t: 64;

[andrew_b]

Closed as duplicate of #3965 .