New src images and switchability

• Added a slew of new text images ranging in sizes of 2x2 to 3x3 to 5x5 to 128x128, and in color variations ranging from single-channels to flat colors to points and ramps of opposing channel-centric colors.
	» All start with `src.` and are PNGs.
	» All within `DrawInQuad/Resources/` dir / project group.
	» Renamed existing `test.png` to `src.eyes.s512.png` and put it with the rest.
	• ViewController now finds all of these by fetching PNG file paths from the `mainBundle` and filtering them down to the ones that start with `src.`, then stores the resulting names into a `_srcPossibilityNames` array ivar (all in a new `- generateSrcPossibilities` method).
• Added an `imageSelectionButton` to Main.storyboard and wired an outlet from ViewController to it and its action to ViewController’s `selectImage:`.
	• ViewController initially sets the text of this button to the name of the currently used srcImage.
	• ViewController responds to the action by showing a QBPopupMenu with the names of each srcPossibility listed.  When one is tapped, `- switchToImage:`/`Named:` updates the button’s text, changes the `_srcImage` reference, and flushes `_srcData`, `_srcWidth`/`Height`, and `_destImage` for later recreation.
	• Added “BlocksKit” and “QBPopupMenu” pods for help with the filtering and custom popup menu.
• Minor: Safety check around dealloc’s `_srcData` release (as well as `switchToImageNamed:`’s).