TEIIDDES-1731: Workaround for flat file connection wizard

* Fragment plugin that replaces the FolderSelectionWizardPage with a
  substitute page that supports a checkbox that can turn off the
  validity check on the folder path entry, allowing 'invalid' paths to be
  inputted.

* Not a perfect solution since the FolderPropertyPage (displayed for the
  properties of an existing connection) cannot be replaced.

* FlatFileStartupOverrider
 * Hacks into the UIManifestExplorer and uses reflection to replace the
   class specified for the wizard page.

* Long-term this should be removed in favour of an upstream eclipse
  datatools fix for this. See https://bugs.eclipse.org/bugs/show_bug.cgi?id=412278
Merge pull request #192 from phantomjinx/master

Workaround NOT a total solution!