Cleanup filetype_make_title() a bit and use it more

* Adds TITLE_NONE, TITLE_SCRIPT and TITLE_DOCUMENT.
* Only a few filetype titles were tweaked but we should review the
  rest as we could use TITLE_SCRIPT and TITLE_DOCUMENT a lot more
  probably.
* Make filetype_make_title() not care about GeanyFiletype type and
  return result instead of internally setting ft state.
Reformat builtin filetype initialization code into tabular format

* Add an initialization function ft_init()
* Add a function-like macro to call ft_init() with shorter arguments
* Search and replace old code with FT_INIT() usage
* Layout into columns and add documentation above