Added different page units, python 3, and changed gitignore, portuguese translation

[riuri]

Page units

• I added a unit chooser with in, mm, and cm on the page size dialog
• The corresponding unit is shown in the status bar

Python 3

• I installed and executed the code in python 3 and manually checked and corrected the differences
• The changes were mostly except statements and relative imports
• My setup is currently using python 3.6.2, but I tested using python 2.7.13 and it installed correctly

.gitignore

• Files generated by autotools were included on the .gitignore file, so now git doesn't complain about not adding those files

Translation

• Since the changes in the page size dialog and status bar introduce difference translatable strings, the translation files were updated
• I also translated those strings to Brazilian Portuguese

If github is not the right place to contribute to gnome, please tell me the directions for doing so

[gnomesysadmins]

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