HackStudio: Open projects after the action tab was created

This change also removes the path argument from the GitWidget
constructor because otherwise, the app wouldn't work now, as it doesn't
yet know the project path.

But it'll be set right away in open_project(), so nothing's lost. :^)

Userland/DevTools/HackStudio/Git/GitWidget.cpp

@@ -22,8 +22,7 @@
 
 namespace HackStudio {
 
-GitWidget::GitWidget(DeprecatedString const& repo_root)
-    : m_repo_root(repo_root)
+GitWidget::GitWidget()
 {
     set_layout<GUI::HorizontalBoxLayout>();