Escape and unescape texts of summary and description fields. 

Fix  Line breaks are not kept #138 on cozy-calendar. 
cozy-ical dependency should be updated in cozy-sync to fix #138 ; and in cozy-calendar to improve calendar import / export compatibility.
it's not obvious to non-coffee reader where parenthesis apply here.
possible solution:
```
value = field?.value or defaults
return helpers.unescapeText value
```