Better DTSTART/DTEND handling

* generalized InvalidResourceException for parsing errors
* only iCals with both DtStart and DtEnd/Duration are processed (DtEnd will be derived by iCal4j when not present in .ics)
* all-day events must last at least one day (fixes #166)
* other DtEnd/Duration rewriting + tests
Version bump to 0.5.8-alpha

* version bump
* introduction of LocalCalendarTest
* always provide DTEND and not DURATION for all-day events (compatibility)
* ez-vcard 0.9.2
Update strings.xml
Update strings.xml
Merge pull request #172 from xphnx/patch-2

Update strings-es.xml
French translation
Merge pull request #174 from poirecahuete/master

French translation
French translation that compiles
Merge pull request #175 from callmemagnus/master

French translation that compiles
Merge remote-tracking branch 'blessed/master'