Display a loading message when searching

Now when searching, a loading message is prepended to the top of
the results. This replaces the old spinner image and allows for it
to be translated across different languages.

The loading message can be styled differently and is passed
through the results formatters.
Built out the translations

This migrates over the required English translations under their
new names.

The "Searching" message has also been adjusted to use "Searching..."
instead of "Loading more results...", which is what it used to
say sometimes.

This also changes the AJAX handler to call `abort` when needed.
Automatically strip diacritics

This adds a dictionary for converting diacritics to a normalized
representation. This dictionary is used in the default matcher.

The code for stripping the diacritics was pulled from the current
implementation in Select2 3.x.