Remove the need to register editors in the action handler

The action handler already knows which editors to handle through the
context. It only needs to receive signals for updating the actions from
the current editor. So there is no need to tell the action handler about
every individual editor. This also removes some noise from the text
editor implementations.

Change-Id: I76dc5b1559cc8cf54ff313e6cdba4e789a3108aa
Reviewed-by: David Schulz <david.schulz@digia.com>
Give TextEditorActionHandler an explicit parent and unify usage.

The action handler implicitly passed ownership to ICore, which is non-
to the action handler. We now consistently create the action handler in
the editor factory, give ownership to the editor factory, and don't hold
a reference to it.

Change-Id: I4372f8de966e3ceff87c06c5528c6b54522c1d57
Reviewed-by: David Schulz <david.schulz@digia.com>
VcsBaseEditor: Use standard method for getting editor settings updates

Change-Id: Ibc07d7b72abb8333905937967e4122b8c7706d37
Reviewed-by: Orgad Shaneh <orgads@gmail.com>