Added Merge All Duplicates button
This could be improved by adding the duplicate detection to the backend. A warning could also be displayed to the user before the merge.
An example of how 3-way duplicates are handled : Transaction 1, 2 and 3 are duplicates (3 is the most recent entry in the database and is therefore the one to keep according to existing code) 1/ [processed] Transaction 3 is kept, Transaction 2 is removed 2/ [skipped] Transaction 2 is kept, Transaction 1 is removed 3/ [processed] Transaction 3 is kept, Transaction 1 is removed
The order of these lines may vary but the result is the same, if the transaction to keep or remove has been removed before, the pair is skipped. After all pairs have been processed, only 1 element of 3-way duplicates remain. This also applies to any amount of duplicates.