Core: Sort document model in a locale aware manner.

Task-number: QTCREATORBUG-12608
Change-Id: If0b9507d31a17cbebfb9fe83fde44738b6e7dcf9
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Fix "Open with" for multiple splits

It was closing all existing editors and opening a single new one in the
"current" split.
Instead, open new editors in all splits where the file was open and
visible.

Change-Id: Iac7238077b2e42937ce54eea65fa1b61dcd07df1
Reviewed-by: David Schulz <david.schulz@digia.com>
Editors: Add "Open with" to open editors and combo box context menus

Change-Id: I67e75220ac86c7fd4d5005424f8b1922e2cbacfd
Reviewed-by: David Schulz <david.schulz@digia.com>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>
PluginManager: Remove hardcoded list of plugins that cannot be disabled

Instead add an optional attribute "required" to the plugin spec. Since
the locator plugin and find plugin are gone, and I don't see a reason to
prevent disabling the text editor plugin, only Core plugin gets the new
attribute set.

Change-Id: I7a380026ea46173cf00afff4213ca1b3a2578434
Reviewed-by: Daniel Teske <daniel.teske@digia.com>