Make debugger console work with all debuggers

Currently the debugger console is only useful with the QML debugger. It is tremendously useful there, though.

With the debugger console you can evaluate expressions only once, and have the result available in further steps, so that you can compare older results with newer ones.

The locals and expressions view also allows you to evaluate expressions, but it will update the expressions in every step, discarding the old values. In order to compare old and new values you have to save the contents somewhere else.

Additionally, I often find myself using the hidden "debugger log" with its input field. This is very hard to use as it mangles multipe text streams into one, and doesn't properly format anything. Also, the default view is is rather cramped if you show the debugger log at the top of the window and some output tab at the bottom. However, giving direct commands to the debugger is obviously a feature I like to have. It should be moved to the debugger console, in order to solve the above problems.