Correctly print complex strings in the debugger

Description

After morley!706 (merged), the debugger shows quote marks around strings to make empty strings appear more intuitively. However, this makes the rendering of strings containing quote marks a bit unintuitive. Also, some characters such as line break (\n) prevent the debugger from showing the remainder of the string.

Steps to reproduce

1. Open complex_strings.tz in the debugger.
2. Set the parameter to \"foo\".
3. Set the storage to \"\".
4. Change the pushed string to "\"aa\" \\\nsomething".
5. Start the debugger.
6. Press "Step Next" two times. The string containing a line break and escaped quote marks will be pushed.

Expected behaviour

1. Quote marks are shown more intuitively, such as escaped, for example.
2. Whatever text is after the line break is shown, as well as the closing quote mark of the string.

Actual behaviour

1. String quote marks are shown unintuitively together with the variable quote marks.
2. Whatever was present after the line break is not rendered.