Implemented Java validations within the UI.

When a user attemps to launch, the configured Java executable will be validated. If it is invalid, we will look for a valid installation. If no valid installation is found, the user will be prompted with an option to install Java. An option to decline needs to be added. If they choose to install, it will download, extract, and update the executable in the config. The game will then be launched.

Also added progress tracking for asset validations, as they can potentially take a bit longer. Showing progress assures the user that the program isn't stuck or broken.

app/assets/js/configmanager.js

@@ -25,7 +25,7 @@ const DEFAULT_CONFIG = {
         java: {
             minRAM: '2G',
             maxRAM: resolveMaxRAM(), // Dynamic
-            executable: 'C:\\Program Files\\Java\\jdk1.8.0_152\\bin\\javaw.exe', // TODO Resolve
+            executable: null,
             jvmOptions: [
                 '-XX:+UseConcMarkSweepGC',
                 '-XX:+CMSIncrementalMode',