Shaderpack settings nearly finalized.

Added saving function, add pack button, drag and drop functionality to the button, ability to
refresh the list of packs.
Added height limit to the dropdown with scrolling. Cleaned up some styles.

app/assets/js/dropinmodutil.js

@@ -208,3 +208,23 @@ exports.setEnabledShaderpack = function(instanceDir, pack){
     }
     fs.writeFileSync(optionsShaders, buf, {encoding: 'utf-8'})
 }
+
+/**
+ * Add shaderpacks.
+ * 
+ * @param {FileList} files The files to add.
+ * @param {string} instanceDir The path to the server instance directory.
+ */
+exports.addShaderpacks = function(files, instanceDir) {
+
+    const p = path.join(instanceDir, 'shaderpacks')
+
+    exports.validateDir(p)
+
+    for(let f of files) {
+        if(SHADER_REGEX.exec(f.name) != null) {
+            fs.moveSync(f.path, path.join(p, f.name))
+        }
+    }
+
+}