Indicate missing files for installed mods

[Krzeszny]

When you manually delete a dll from rml_mods or rml_libs, Resolute has no way of knowing you've deleted it and still shows it in Installed Mods. Even clicking Discover Installed doesn't remove deleted mods from the list.

[Gawdl3y]

This is intentional since a file could be accidentally deleted or deleted by something else unknowingly. The reinstall button would allow correcting this in that case. What may be useful, however, is an indicator that some files are missing for a mod that's supposed to be installed.