Import - Modify Duplicate Handling Options

We need to suppress (hide) an existing duplicate handling option and implement a new one.

1. Remove the 'Replace' choice from the 'On duplicate entries' field in Upload.php and remove the description of this choice in Upload.tpl

[We are hiding this option for now because we're not sure it's needed AND it would currently cause all relationship, group memberships, activity_history, etc to be LOST for the contact being replaced - because replace is actually delete+insert. This is pretty destructive and shouldn't be offered unless there's a clear need presented by users at some later date.]

2. Add a new dupe handling choice. Option label = 'No Duplicate Checking'. This should be last option in this set of radio buttons.

2.1 If this value is selected, then either bypass or ignore any duplicate contact errors and insert all valid records.

2.2 Add 'explanation' in Upload.tpl for this option:
'No Duplicate Checking: Insert all valid records without comparing them to existing contact records for possible duplicates.'

NOTE: This choice does NOT affect the detection/processing of 'conflicts'. Conflicts are records w/in the import file which have the same email address. These should be handled as 'errors' - as now.