Propose better captions for the messages (jquense#911)

Having uncapitalized messages turns the calendar ugly in the presentation.

I also propose putting font awesome chevrons on the previous and next. What do you think.

src/utils/messages.js

@@ -2,17 +2,17 @@ let defaultMessages = {
   date: 'Date',
   time: 'Time',
   event: 'Event',
-  allDay: 'all day',
-  week: 'week',
-  work_week: 'work week',
-  day: 'day',
-  month: 'month',
-  previous: 'back',
-  next: 'next',
-  yesterday: 'yesterday',
-  tomorrow: 'tomorrow',
-  today: 'today',
-  agenda: 'agenda',
+  allDay: 'All Day',
+  week: 'Week',
+  work_week: 'Work Week',
+  day: 'Day',
+  month: 'Month',
+  previous: 'Back',
+  next: 'Next',
+  yesterday: 'Yesterday',
+  tomorrow: 'Tomorrow',
+  today: 'Today',
+  agenda: 'Agenda',
 
   noEventsInRange: 'There are no events in this range.',