I18n work for platform UI parts

In this issue we will externalize relevant strings from all UI-related plugins in the platform. We do this selectively only for UI plug-ins for now, not for all plug-ins as there is too much work

To Do:

• Externalize relevant strings to message.properties files from Java code
• Externalize relevant strings from plugin.xml and fragment.e4xmi files to OSGI-INF/l10n/bundle.properties
  • Project context menu Plug-in Tools -> Externalize Strings helps with plugin.xml
  • Fragment.e4xmi editor has Externalize Strings in its context menu as well to help
• Ignore irrelevant string in UI plug-ins to prevent us from repeatedly going through the same strings