Prefix Translation Keys

Use `pageflow.editor` instead of only `editor` etc.
Extract Texts into Translations.

Flatten all translations into one file per locale.
Add CSS Class to name Column of Admin Table

Feature spec depends on exact class name.
Localize Editor Help View
Remove Texts from Images
Make Locale Configurable for Users

Switch used locale in admin based on user setting.
Make Locale Configurable for Entries

Render entries with locale configured in Editor.
Add configure_active_admin call to active admin generator
Reload Editor after Locale Change

Their is no mechanism at the moment to fetch page templates for a
different locale.
Allow Changing Available Locales via Configuration
Merge pull request #220 from tf/i18n

Internationalization