Bug fixes and enhancements

[x] Display list of Centers when creating a station, currently the list is empty.
[x] Display Success message after station creation.
[x] Confirm the station can be seen in the centers list after creation.
[x] Fix forms not received table search functionality.
[x] Remove choices option from gender field.
[x] Make Barcode, center code, station number and race type unique per result form to prevent duplicate result form creation.
[x] Add total number of forms processed column on staff metrics column.

onaio / tally-ho