update the behavior of the run and debug buttons

We should update the behavior of the run and debug buttons to address some UX issues:

• the run button should be changed from executing flutter run --release to flutter run (just like the current debug button) (#445)
• the run button should not set breakpoints and not break on exceptions (it’s the same as the debug button, but without debuggability)
• we contribute a hot reload and a restart app button to the run toolbar; these should likely be visible when the currently selected config is hot reloadable (or when the device chooser is visible)
• when an app is executing, the run and debug buttons become disabled (the launch config reports that it can’t run if any running apps were launched from that config)

[alexander-doroshko]

Make sure that you do not modify Run/Debug icons and behavior if currently selected run configuration in the combo box is not the one that you want to hot reload or whatever. It is a valid use case:

• select ‘MyFlutterApp1 (debug)’ in the combo box, Debug it
• select not related ‘Some Java Server’ run config, Run or Debug it
• etc.
• select ‘MyFlutterApp1 (debug)’ again. Hot reload it

[devoncarew]

I updated the main description above to list what we’ve already done here and what more is planned.