Debugger: Add breakpoint commands for LLDB backend

Commands needs to be given in Python, i.e. something like

    import time
    print time.asctime()
    for i in range(1, 10):
         print(i)

works.

Task-number: QTCREATORBUG-15585
Change-Id: I7724617e4bbe85a717ae78b21014e2b55c4089c8
Reviewed-by: Alexandru Croitor <alexandru.croitor@theqtcompany.com>
Reviewed-by: hjk <hjk@theqtcompany.com>

src/plugins/debugger/breakhandler.h

@@ -113,6 +113,8 @@ public:
     QString expression() const;
     void setExpression(const QString &expression);
     QString message() const;
+    QString command() const;
+    void setCommand(const QString &command);
     void setMessage(const QString &m);
     BreakpointType type() const;
     void setType(const BreakpointType &type);