[request] System to Merge duplicate accounts

[Floris]

After merging quite a bit of sites I ended up with quite a bit of multiple accounts.

imported_USER and USER.

A page where they list the results of imported_MATCH and MATCH with behind it their email address (for confirmation) and a button [merge] which then merges the accounts.

This way I can quickly browse through known usernames and clck merge if I confirm they're the same user and need to be merged.

Or of course a global option at the top to auto merge all (selected) if the username matches imported_MATCH and if they both have the same email address.

for 3.6