Fix mo field size

The translation strings for some languages are not loaded, because the database truncates the locale to 2 characters. This patch increases the field size to 5 characters (enough to accommodate for all locales in php/presets.php). Not sure how current databases should be upgraded (I have no experience with wordpress plugins).

In addition, I have also fixed some notice-level warnings about undefined variables/indexes, and one deprecation notice. This gives a cleaner output in [Vagrantpress][1]. Feel free to leave this commit out of the merge.

[1]: http://vagrantpress.org/