Add a max-width feature/option to columns

[xiaohutai]

If you have very long labels, then you get very broad columns.

My recommendation is to use keys like foo.bar.baz as much as possible anyways; but it still allows for very long values.

A few ideas:

• have a max-width column set for key column and language columns in configuration file
• add a button that fits the table on the current screen's viewport (minus left bar) by setting the column widths proportionally. (could toggle between expand and fit-on-screen)