Export and import of plugin archives

[nilskruthoff]

• Added an shared rust api that supports native share dialogs in Windows and MacOS
  • included microsoft and macos rust dependencies that wrap native functions (they are part of tauri already)
• Added a share button for plugins that uses native share dialogs to each non-internal, non configured plugins
• Added an import button to the plugins page to install plugin archives directly from the disk
• Introduced an own file extension .mwplugin for plugin zip files
• Refactored PluginSystem zip functionality into own class PluginArchive.cs