Redesign of simulator switching system

[ra3xdh]

Current simulator switching system has some limitations and would benefit from redesign. The simulator switching system should meet the following requirements:

• It should be possible to switch simulator without requirement to restart the application
• Place a "simulator" drop-down list someweher on visible place in the GUI
• This drop-down list should contain only properly configured simulators which binaries are found in the system. The user cannot switch to invalid simulator by mistake
• After the simulator is switched, the incompatible devices become hidden. The application restart will be not needed anymore. If the incompatible devices are already added on the schematic, it should be marked by some way. I propose black cross for this purpose. Red cross is for disabled devices, green gross for shorted devices.
• The simulator binaries location paths could be configured from Simulation->Select simulator menu.

[ra3xdh]

The requested features are implemented by #283