Git: stashes is added.
StashesWidget is added.
MainWindow: Stashes dock is added.
Small fix.
Git: pop stash is added.
StashesWidget: menu is added. Pop is added.
MainWindow: add stashes menu into main menu.
Git: save_stash is added.
StashesWidget: save action is added.
Merge branch 'develop' into feature/AddStashesWidget
Merge branch 'develop' into feature/AddStashesWidget
Git: class Stash is added.
Git: drop_stash is added.
StashesWidget: drop action is added.
StashesWidget: set actions enabled.
Merge branch 'feature/AddStashesWidget' into develop