As an editor I want Senses to be taken into account when merging Lexemes in order to have a complete merge and not lose any valuable information when merging two Lexemes.
**Problem:**
Lexeme merging so far only takes into account the Lexeme- and Form-level data and not the Senses data.
**BDD**
GIVEN a source and a target Lexeme that should be merged
AND the source Lexeme contains at least one Sense
WHEN merging the source Lexeme into the target Lexeme
THEN the Sense data is removed from the source Lexeme
AND each individual Sense including Glosses and statements is added as a new Sense to the target Lexeme
GIVEN a source and a target Lexeme that should be merged
AND the source or target Lexeme contain at least one Sense with a statement linking to the other one
WHEN trying to merge the source Lexeme into the target Lexeme
THEN the merge is not done
AND an error message "Failed to merge Lexemes, please resolve any conflicts first. Error: Lexemes link to each other in a statement." shown
**Acceptance criteria:**
* no Sense data is lost in a merge
* new IDs in the target Lexeme for the Senses are acceptable for now
* if the source and target Lexeme link to each other in a statement on a Sense then the merge is blocked
* works via SpecialPage and API