removes custom implementation of estimated hours

It existed in order to allow for the inheritance of permissions from
other users. This feature was never completed and has been removed for
some time now. As such, it is easier to rely on the core to provide the
correct values.
also show spentTime value if the user has view_own_time_entries
Merge pull request #114 from finnlabs/feature/remove_custom_estimated_hours

removes custom implementation of estimated hours