Refactor application structure and initialize core components

I decided to rewrite the program taking into account the experience gained.

internal/controller/convertor.go

@@ -0,0 +1,8 @@
+package controller
+
+import "git.kor-elf.net/kor-elf/gui-for-ffmpeg/internal/gui/view"
+
+func (c *controller) convertor() {
+	content := view.Convertor()
+	c.window.SetContent(content)
+}