add emacs integration files for code formatting

Adds emacs integration lisp files to enable the use of LHCb's clang-format and yapf formatting tools in emacs. Adds three files, one for clang, one for yapf and a third that loads them both. Users only need to load this third one, with

(add-to-list 'load-path (getenv "EMACSDIR"))
(require 'lb-format)

where EMACSDIR is then an environment variable set by the LbEnv environment, to point to the directory containing the released lisp files.

Not everything is completely perfect.

I would like to use the emacs specific EMACSLOADPATH env var, which potentially would mean the first line above would not be required in the user's ~/.emacs file. But all my attempts to get this to work broke emacs, so for the moment I am using the above.

Also currently the emacs commands for formatting c/c++ and python are not the same lb-format-c and lb-format-py respectively. It would be nice to have a single command, which then does the right thing depending on the file mode, but my lisp skills have not been up to getting this working...