Early draft of path rendering.

Full of ugliness and sin. Very hardcoded. So hacky. Much work to do.
- Don't draw action line if the tagged sector of a line special is adjacent to that line
- Made the arrow lines a bit thinner
Merge branch 'master' of https://github.com/sirjuddington/SLADE
Made code compile again.
GFX entry panel fixes

Converting to paletted PNG from the GFX entry panel removed transparency
because when writing PNG it relied on the status of the tRNS menu item
rather than the content of the image, and converting from the GFX panel
did not update the PNG-related menu items.
Optimizing PNG from the GFX panel marked it as modified, prompting for a
save, which caused rewriting the entry and destroying any optimization
done by external tools.
Make jpeg image format valid for texturex patches
Tweaked the look of vertex hilight/selection overlays (when point sprites are enabled)
Path rendering work, continued.

Less hardcodedness.
Merge branch 'master' of https://github.com/sirjuddington/SLADE
Path rendering work, continued.

Highlighted interpolation points are no longer rendered as being tagged
by themselves.
Dragon pathing finished!
Factorized "tagged" lookup.
Fix some configs.