Addressed some Scala 2.10 compiler warnings

This commit removes some unnecessary implicit conversions and many uses of
deprecated functions and features
Don't use an unnecessary Option[A] wrapper in the UIUtils.exec method
Export all but the Java-specific package from the Kopitiam plugin

This highly-experimental change (which, you should note, comes with no API
guarantees of any kind whatsoever) should make it possible to move the Java
functionality into a new plugin
Attempted to update the TODO file a bit

The new TODO file contains some observations about the current state of
Kopitiam, and the TODO.old file is a copy of TODO.org with a few outdated
remarks removed
Perform an extra check when trying to enable a SaveProofCertificateHandler

The existing check assumed that each JavaEditorState always has an
associated compilation unit, but this isn't the case if VerifyMethodHandler
has never been executed for an editor
Made the automatic reveal behaviour of CoqStepBackRunner optional

This commit also modifies CoqProofReconcilingStrategy to use this new
functionality. As a consequence, automatic backtracks no longer reveal
anything