Issue #22 - Use Scale Independent Pixels for text sizes

* Convert dp units to sp, in order to be scaled based on users
configuration.
* Use a bare minimum of 14sp, in order to increase the readability in
some cases.
* Match Settings and Preferences screens text sizes.
Issue #20 - Enable locale configuration from within the app

* Provide Locale selector under Settings > Preferences
* Add correspondent Strings
Fix typo