Extract DictionaryFactory

 * Adds in a locale preference for main dictionary
 * If we have a dictionary for the curent local then that is set the default otherwise US is chosen
 * Moves Locale handling code to LocaleUtils
 * Changes startup process due to strange SWT access error when running the tycho tests
 * Simplfies Checker to just have the three dictionaries and sync on this
 * Extracts dictionary creation to a DictionaryFactory
 * Fixes error thrown from PersistentSpellDictionary after clearing, by creating an empty file


see #14
see #8

 * Remains to sort out the Locale preference setting
Adds other eclipse versions to the pom for as-hoc testing
Add ability to enable and disable the spell checking

 * Improves the edior tracker to listen to new windows.
 * Add documentation to clarify behaviour of Editor tracker
 * Fixes the behaviour of the tracker to match that required and better deactivate the editors
 * Adds clear to the engine for disabling the spelling
 * Improves preference page layout

fixes issue #16