Added Plugin support (#102)

* Build refactoring and initial plugin support

* Possibly fixed linux / mac build

* Added libdl to libglad build script

* Add glfw to imgui dependencies

* Refactored common functionality into "libimhex" for plugins

* Added plugin loading and example plugin

* Added proper API for creating a custom view and a custom tools entry with plugins

include/views/view_help.hpp

@@ -19,8 +19,8 @@ namespace hex {
         ViewHelp();
         ~ViewHelp() override;
 
-        void createView() override;
-        void createMenu() override;
+        void drawContent() override;
+        void drawMenu() override;
 
         bool hasViewMenuItemEntry() override { return false; }