Add PT translation to TikZ backend

For the translation we use gettext.

Note: The *.mo files have been add to make easy the installation.
Update file name
Update translation
Merge pull request #57 from r-gaia-cs/i18n

Internationalization and localization
Add flag for translation of axis label

Related with PR #40.

Add flat `--lang` to select the language of the axis labels. The
language of the label can be different from the system language.

**Note**: No option to user defined label will be provided right
now.

**Note**: Probably this not work with Windows.
Merge pull request #56 from r-gaia-cs/lang

Add flag for translation of axis label