Fix instant-recalc property change handling

Despite the actual value, only the gswe_timestamp_calculate_all() was called.
Add GsweTimestamp::julian-day property

It was somehow missing from the property list
Remove unnecessary notifications upon GsweTimestamp creation
Merge branch 'master' into testing
Update .gitignore with more testing related files
Make TimestampValidity public with name GsweTimestampValidityFlags
Remove GLib-specific names from configure.ac

Code coverage reports were migrated from GLib sources, and some names remained