Minor Select.js refactor

[yuri-sakharov]

Select.js code is inconsistent, some times uses var, some times const, let. Present unused prop. 2 methods I moved outside of the class and alphabetically order.

[coveralls]

Coverage increased (+0.02%) to 94.134% when pulling 9e003b7 on yuri-sakharov:refactor/select-1 into d2a3afd on JedWatson:master.

[coveralls]

Coverage increased (+0.02%) to 94.134% when pulling b09afb9 on yuri-sakharov:refactor/select-1 into d2a3afd on JedWatson:master.

[coveralls]

Coverage increased (+0.02%) to 94.142% when pulling 8a5689f on yuri-sakharov:refactor/select-1 into d2a3afd on JedWatson:master.

[coveralls]

Coverage increased (+0.02%) to 94.142% when pulling bb8e7b0 on yuri-sakharov:refactor/select-1 into d2a3afd on JedWatson:master.