Handle panics without crashing the app

[alexwkleung]

When a user does an action that causes a panic (Rust side), it crashes the app.

Since this isn't the ideal behaviour, I would like to handle this preferably as an alert of some sort on the JS side. However on the Rust side, I'm not sure if handling errors using the panic! macro is appropriate for all cases.

In vague terms:

panic! is meant for unrecoverable errors and it destroys the entire stack in memory after it gets executed, causing the app to crash by default

I'll have to take a closer look at this later on. Without handling these edge cases correctly, the flow of the app will diminish and the UX won't feel as robust.

[alexwkleung]

On the front-end, I make sure to return early when a supposed panic could happen. A dialog appears as well.

Closing since v0.2.0-dev-5.0 will have these changes. Might not be 100% but it's a good start.

Of course I want to make the back-end more rigid in the future.