tidying up, tooltips, l10n

1) Tidying up text on the admin page.
2) Putting tooltips in the meta box instead of lots of visible text (to
tidy up things a bit and avoid repeating the explanation when another
input is added for a multivalue field.
3) Full localization into Portuguese.
If this commit is accepted, maybe we should have a different version
number? x.x.1?
Merge pull request #5 from Tintazul/master

tidying up, tooltips, l10n