Move them change handling out of the package

Now MEF composition doesn't happen in Package.Initialize anymore.
At least package load has a higher chance to succeed and MEF composition
error no longer makes the whole extension unusable.

Related to #583.
Remove an unused field
Merge pull request #584 from dungpa/fix-package-load

Move theme change handling out of the package
Generic type parameters shouldn't be escaped - fixes #585
Merge pull request #586 from forki/Rename

Generic type parameters shouldn't be escaped - fixes #585
Create a rename suggestion list

  - spell checking
  - thesaurus
Convert suggestion sequence to naive observable
Make the suggestions an observable
Add plural and singular forms to the suggestions
Suggest parts of the Identifier
Fix casing for type and variable