[feature] Set default header and avatar for API accounts to GtS ones (#799)

* validate web-asset-base-dir

* move default icons into converter

* always ensure avatar + header on api accounts

* update tests

* add default header

* don't return error from web module creation anymore

* tidy a bit

* use pngs for default avatars rather than svgs

internal/config/validate.go

@@ -62,6 +62,11 @@ func Validate() error {
 		errs = append(errs, fmt.Errorf("%s must be set to either http or https, provided value was %s", ProtocolFlag(), proto))
 	}
 
+	webAssetsBaseDir := GetWebAssetBaseDir()
+	if webAssetsBaseDir == "" {
+		errs = append(errs, fmt.Errorf("%s must be set", WebAssetBaseDirFlag()))
+	}
+
 	if len(errs) > 0 {
 		errStrings := []string{}
 		for _, err := range errs {