Add panorama version of autosave indicator

[vrad-exe]

This adds a Panorama version of the Portal 2 save indicator, intended to replace the VGUI one. I've tried to match the style of Portal 2's version as closely as possible, aside from using P2CE's font.

The Panorama save indicator is the bottom one in the image, top is VGUI for comparison:

It also adds an Autosave Indicator setting to the interface options menu, which controls whether or not the indicator is shown for autosaves.

However, there are a few changes that need to be made on the C++ side of things before this is merged:

• The spinner is an AnimatedImageStrip, which seem to have a bug where they permanently stop animating when the game is paused (#183) Worked around
• It can't accurately represent how long the save actually takes because Panorama only fires an event when the save starts (#184). I've currently made it show "saving" for 1 second and "saved" after that as it fades out which is similar to what Portal 2 does, but that's only because of weird console requirements, ideally P2CE's version should accurately show the time it takes to save (even if that ends up being near-instant in most cases).

Also, currently the indicator shows different text for autosaves compared to manual/quick saves, but I'm not sure if I want to keep this or not - it looks kind of weird and I don't think any other source games with autosave indicators do this. I've also thought about deviating from Portal 2 by making the spinner get replaced with a "save complete" icon after the save operation finishes, but someone else would need to make that icon, I'm not much of an artist.

[iamsirenstorm]

Something to note, we have an internally registered Save Indicator panel already from Revolution. I actually didn't know this and found it on accident when pulling up the other save files in the codebase. It's called HudSaveIndicator.

So you can drop the custom panel registration, and then change where you reference SaveIndicator to HudSaveIndicator:

Suggested change

	<Panel class="save-indicator">
	<AnimatedImageStrip
	id="Spinner"
	animating="true"
	defaultframe="0"
	frametime="100ms"
	src="file://{images}/hud/spinner_saving_strip.tga"
	scaling="stretch-to-cover-preserve-aspect"
	/>
	<Label class="save-indicator__label" id="StatusLabel" text="#PORTAL2_Hud_GameSaved" />
	</Panel>
	<HudSaveIndicator class="save-indicator">
	<AnimatedImageStrip
	id="Spinner"
	animating="true"
	defaultframe="0"
	frametime="100ms"
	src="file://{images}/hud/spinner_saving_strip.tga"
	scaling="stretch-to-cover-preserve-aspect"
	/>
	<Label class="save-indicator__label" id="StatusLabel" text="#PORTAL2_Hud_GameSaved" />
	</HudSaveIndicator>