Add Start at Login Option (Windows and Linux implemented, MacOS stubbed)

This merge request adds the following:

1. A new class AutoStart, designed to add login startup entries for Linux (FreeDesktop autostart) and Windows (Shortcut File).
1. CLI options to enable, disable and check for autostart. (--autostart-enable, --autostart-disable and --autostart-check). e.g. OpenRGB.exe --autostart-enable "--startminimized --server --profile Blue" --nodetect --noautoconnect
1. UI options to enable "Start At Login" with several other options (see screenshots in Comments)

Tested on KDE Neon and Windows 10 x64 (x64 build).

Commits squashed and amended for code style by Adam Honse <calcprogrammer1@gmail.com>

AutoStart/AutoStart.cpp

@@ -0,0 +1,16 @@
+#include "AutoStart.h"
+
+/*-----------------------------------------------------*\
+| Common AutoStart Implementation                       |
+| Public Methods                                        |
+\*-----------------------------------------------------*/
+
+std::string AutoStartInterface::GetAutoStartFile()
+{
+    return(autostart_file);
+}
+
+std::string AutoStartInterface::GetAutoStartName()
+{
+    return(autostart_name);
+}