As an editor I want to be able to merge two Lexemes in order to eliminate duplicates.
**Screenshots:**
Before merge of two items:
{F22636219}
After successful merge of two items:
{F22636079}
**BDD**
GIVEN I have two Lexemes that represent the same word
WHEN I go to Special:MergeLexemes
AND enter their IDs
AND I click "merge Lexemes
THEN the source Lexeme is emptied and replaced by a redirect to the target Lexeme
AND the statements of the source Lexeme are added to the statement section of the target Lexeme unless identical statements already exist
AND the Forms of the source Lexeme (including their statements) get added as new Forms to the target Lexeme (unless they are have identical representation and grammatical features)
AND I get a confirmation message saying "L123 was merged into L1234 and redirected."
**Acceptance criteria:**
* A new SpecialPage Special:MergeLexemes exists and can be used to merge two Lexemes.
* After a merge the source Lexeme contains a MediaWiki redirect to the target Lexeme (just like it is done for items).
* After the merge I can go to the URL of the source Lexeme and am redirected to the target Lexeme.
* If there are identical Forms (same representation and grammatical features) in each Lexeme then the statements for that Form get added to the existing Form.
**Notes:**
* Blocking of specific bad merges is not covered in this ticket.
* Redirecting on the Form level is not to be done at this point - only the Lexeme level
* Text and design on Special:MergeLexemes should be the same as on Special:MergeItems with s/Items/Lexemes. The text for the longer message should be "If you merge two Lexemes, all representations, Forms, Senses and statements will be moved from one Lexeme to the other."
**Open questions:**
* What happens on items when both have the exact same statement? Do they get duplicated or does this statement get ignored during the merge?