Bug 32764 and I18N/L10N chapter update
Bug 32764 highlights a need to refer solely to the Koha Wiki to install languages. It also points to inconsistencies in the dateformat preference description.
- I rephrased the dateformat preference description.
- I deleted the command and instead created a note with a link to the Koha Wiki for both languages system preferences.
- I updated the formatting of all sections on the i18npreferences.rst page according to the ReStructuredText - Tips and Tricks.
- I updated the two screenshots.