Use uniform date format in tests

Part of work on #4416.
Reset default date format on login error

When unlogged, the default format is MM/dd/yyyy.

Part of work on #4416.
Get GC custom date on every succesful login

Part of work on #4416.
fix #4416: new preferences page on geocaching.com
Do not accept log entries without valid date
Merge branch 'issue-4416' into upstream

Conflicts:
	main/src/cgeo/geocaching/connector/gc/GCLogin.java