Add Plugins tab to settings for installing, enabling, disabling, and removing plugins

* Rework Plugin Manager so that plugins can be loaded after initialization
* Use a callback function to add plugin tabs to the dialog
* Install button lets you choose plugin file, copies it to plugins directory, and immediately loads it
* Remove button deletes selected plugin file from plugins directory - need to add a means to unload it first

PluginManager.h

@@ -11,10 +11,29 @@
 #include <string>
 #include <iostream>
 
+typedef struct
+{
+    OpenRGBPluginInterface*     plugin;
+    std::string                 path;
+    bool                        enabled;
+} OpenRGBPluginEntry;
+
+typedef void (*AddPluginTabCallback)(void *, OpenRGBPluginInterface* plugin);
+
 class PluginManager
 {
 public:
-    std::vector<OpenRGBPluginInterface*> ActivePlugins;
+    PluginManager(bool dark_theme);
 
-    void ScanAndLoadPlugins(bool dark_theme);
+    void RegisterAddPluginTabCallback(AddPluginTabCallback new_callback, void * new_callback_arg);
+    void ScanAndLoadPlugins();
+    void LoadPlugin(std::string path);
+
+    std::vector<OpenRGBPluginEntry> ActivePlugins;
+
+private:
+    bool dark_theme;
+
+    std::vector<AddPluginTabCallback>   AddPluginTabCallbacks;
+    std::vector<void *>                 AddPluginTabCallbackArgs;
 };