[DS-1751] Some edited English message texts

https://jira.duraspace.org/browse/DS-1751

I would particularly appreciate other eyes on the places where I replaced hardcoded Portugese "Bloqueado" with an <i18n:text> element.  I *think* I did this properly but should be double-checked by someone with more experience in this area.

There is a very fine distinction between "mandatory" and "required", but I made the change because I thought it seemed just as firm but less commanding.

Comments would be welcome on any of my changes.