Draft: Rely on translations for stop word lists

From the main commit:

libtracker-common: Replace stop word list with translatable string

Maintaining a separate set of language-dependent stop word lists
has shown to be the perfect way to bury the feature. These lists
were added on 2006 by commit 7e65e4d14 and are pretty much unchanged
ever since.

In order to improve the situation, tap into our own pool of
i18n wisdom and implement stop words over a translatable string.
This will hopefully result in this feature working for more
languages than few ones we did handle.

While at it, heavily trim the english stop word list, from 595 to
127 terms.

This comes with a number of cleanups and improvements to actually make our stop words infrastructure apply to something else than English.