specify timezone in configuration (closes foodcoops#282)

config/app_config.yml.SAMPLE

@@ -37,6 +37,8 @@ default: &defaults
   # In case you really want foodsoft in a certain language by default, set this to true.
   # When members are logged in, the language from their profile settings is still used.
   #ignore_browser_locale: false
+  # Default timezone, e.g. UTC, Amsterdam, Berlin, etc.
+  #time_zone: Berlin
 
   # price markup in percent
   price_markup: 2.0

config/locales/en.yml

@@ -504,6 +504,7 @@ en:
       pdf_font_size: Font size
       pdf_page_size: Page size
       pdf_add_page_breaks: Page breaks
+      time_zone: Time zone
   deliveries:
     add_stock_change:
       how_many_units: 'How many units (%{unit}) to deliver? Stock article name: %{name}.'

config/locales/nl.yml

@@ -487,6 +487,7 @@ nl:
       pdf_font_size: Tekstgrootte
       pdf_page_size: Paginaformaat
       pdf_add_page_breaks: "Nieuwe pagina's"
+      time_zone: Tijdzone
   deliveries:
     add_stock_change:
       how_many_units: 'Hoeveel eenheden (%{unit}) leveren? Voorraadartikel: %{name}.'