Improving application startup flow.

Major improvements to distribution index loading.
Implemented new transitional UI for startup.
If **no** distribution index is loaded on startup, completion of startup will be prevented and the user will be shown a message displaying the issue.
Launch errors are now shown as overlays.
Many more minor fixes and enhancements.

app/assets/js/assetexec.js

@@ -41,6 +41,8 @@ process.on('message', (msg) => {
             if(res instanceof Promise){
                 res.then((v) => {
                     process.send({result: v, content: msg.content})
+                }).catch((err) => {
+                    process.send({result: v, content: msg.content})
                 })
             } else {
                 process.send({result: res, content: msg.content})