Allow config files to be placed under the memstick.

This way, they can be configured more easily on Android, etc.
Respect ini file path on reset settings.

This is the easiest way to force settings to the memstick, but it means
erasing the existing ones.
Rename flashDirectory to flash0Directory.
Use ms0:/PSP/flash0/font/ as an override for fonts.

This won't work for games that use flash0:/ directly, but if they just use
the default fonts (which is common), it will work fine.
Also respect Windows absolute paths.
Load custom shaders from ms0:/PSP/shaders/.
Override shaders by name.
Minor warning fixes.
Merge pull request #4148 from unknownbrackets/config-files

Allow config files and fonts to be on the memstick