Update messages_es.properties

Commits: 1ca05be, c481d8a, 305b76a/c2f4076, 00271e8, f062600, e3e7af4, 73437d4, 39ed614, bcde536, 45b2bc9, b57f926, e84cbab

Capitalized words changed to "sentence case" (still incomplete).
Merge pull request #424 from AlfredoRamos/patch-1

Update messages_es.properties