Add simulator plugin selection on startup

[ltoenning]

Currently, we load all available plugins at start time. To reduce complexity and avoid loading unused plugins, the user should be asked on startup which simulator to choose. Additionally there could be a selection like "Remember my choice" when regularly using the same simulator.

This also fixes an issue when loading plugins using SimConnect. Right now, the first plugin loaded using SimConnect decides which SimConnect version gets loaded (either P3D or MSFS). Hence, its possible that the P3D SimConnect version is used when using MSFS and vice versa.

• Add user selection when starting swiftgui with a list of all found simulator plugins
• Only load the plugin selected by the user (see pluginmanagersimulator.cpp
• Add a "Remember my choice" button