Added Open Recent functionality to File menubar item
Added new editor setting for Startup Mode to dictate if it'll open the most recent level edited or the blank level, instead of utilizing a game UI control for level selection.
Properly re-enabled the handling for the forceSidebarToSide setting to track to the setting value
This makes some tweaks to the engine to support this, specifically, it tweaks the hardcoded shaderpaths to defer to a pref variable, so none of the shader paths are hardcoded.
Also tweaks how post effects read in texture files, removing a bizzare filepath interpretation choice, where if the file path didn't start with "/" it forcefully appended the script's file path. This made it impossible to have images not in the same dir as the script file defining the post effect.
This was changed and the existing template's post effects tweaked for now to just add "./" to those few paths impacted, as well as the perf vars to support the non-hardcoded shader paths in the engine.
