Fix temporary models for relations.

ForeignKeyJsonConverter creates temporary models for relations when they
don't exist. However, the change in 64362cd changed the default
ModifiedAt for models, thus the temporary models became the dominant
ones and sync couldn't update them with correct data from server.
Make log time entries continuable.

Android system was making the list items in the log list view
non-clickable due to the presence of the Edit button. Added
focusable="false" attribute to disable that and allow user to click the
row.
Fix continuing historic time entries.

All of the time entries in the AllTimeEntriesView aren't guaranteed to
be persisted. Thus need to make sure that the entry that the user is
trying to continue is marked as IsPersisted beforehand.