Add pt-BR translation for PNG error messages

[brunolmfg]

I'm translating the error messages of several modules. The first is for validation and metadata extraction on PNG files. The added properties file is UTF-8 encoded.

That's a contribution by Hacktoberfest and the OPF Document Hack Week.

See #474.

[codecov]

Codecov Report

Merging #490 into integration will increase coverage by 3.59%.
The diff coverage is n/a.

@@                Coverage Diff                @@
##             integration     #490      +/-   ##
=================================================
+ Coverage          45.77%   49.36%   +3.59%     
+ Complexity          1050      969      -81     
=================================================
  Files                 57       55       -2     
  Lines               9150     7666    -1484     
  Branches            1686     1392     -294     
=================================================
- Hits                4188     3784     -404     
+ Misses              4416     3422     -994     
+ Partials             546      460      -86

Impacted Files	Coverage Δ	Complexity Δ
...e/src/main/java/edu/harvard/hul/ois/jhove/App.java	62.5% <0%> (-37.5%)	8% <0%> (-1%)
...java/edu/harvard/hul/ois/jhove/TextMDMetadata.java	64.28% <0%> (-12.25%)	22% <0%> (-4%)
...in/java/edu/harvard/hul/ois/jhove/InfoMessage.java	41.17% <0%> (-11.77%)	4% <0%> (-1%)
...in/java/edu/harvard/hul/ois/jhove/HandlerBase.java	67.35% <0%> (-4.08%)	46% <0%> (+6%)
...src/main/java/edu/harvard/hul/ois/jhove/Agent.java	45.52% <0%> (-1.3%)	13% <0%> (-1%)
...main/java/edu/harvard/hul/ois/jhove/JhoveBase.java	41.79% <0%> (-1.28%)	41% <0%> (-2%)
...a/edu/harvard/hul/ois/jhove/NisoImageMetadata.java	74.64% <0%> (-1%)	175% <0%> (-7%)
...c/main/java/edu/harvard/hul/ois/jhove/RepInfo.java	56.15% <0%> (-0.77%)	38% <0%> (-2%)
...va/edu/harvard/hul/ois/jhove/AESAudioMetadata.java	87.56% <0%> (-0.55%)	37% <0%> (-1%)
...ain/java/edu/harvard/hul/ois/jhove/ModuleBase.java	50.69% <0%> (-0.11%)	70% <0%> (-3%)
... and 13 more

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