Index fixes and performance improvements (fixes #223, #224)

- Fixed creation of duplicate index entries when importing from CurseForge (fixes #224)
- Automatically remove duplicates in index
- Fixed `packwiz serve` with a custom `--pack-root` argument (fixes #223)
- Fixed `packwiz serve` with a custom index.toml location
- Cleaned up internal serving code, added comments and better errors
- Refactored path handling code
- Improved refreshing/exporting performance
- Factored out duplicated exporting logic
- Replaced GetAllMods calls with cleaner LoadAllMods calls and made the former private
- Improved variable names in update command
- Improved handling of aliassed files
- Changed CheckUpdate to take references to metadata
- Removed the ability to use an absolute path to the index file (that probably didn't work anyway)
- Behaviour change: order of entries in exported files may be random

modrinth/modrinth.go

@@ -386,9 +386,12 @@ func getBestHash(v *modrinthApi.File) (string, string) {
 
 func getInstalledProjectIDs(index *core.Index) []string {
 	var installedProjects []string
-	for _, modPath := range index.GetAllMods() {
-		mod, err := core.LoadMod(modPath)
-		if err == nil {
+	// Get modids of all mods
+	mods, err := index.LoadAllMods()
+	if err != nil {
+		fmt.Printf("Failed to determine existing projects: %v\n", err)
+	} else {
+		for _, mod := range mods {
 			data, ok := mod.GetParsedUpdateData("modrinth")
 			if ok {
 				updateData, ok := data.(mrUpdateData)