Jagex Account Selection

[Z-Kris]

The proxy tool currently only supports loading an existing Jagex Account credentials file if it has been exported by RuneLite. There is no way to opt out of this without just deleting the respective credentials file, nor is there any way to swap between Jagex Accounts.
We should add a pop-up window after client selection that asks how the client should be booted up, with the options being:

1. No Jagex Account - this option will just launch the client as-is, without passing in Jagex Account information. Users can login with an username/email and password.
2. A Jagex Account. This option should load all stored credentials files in the proxy home and list them, allowing users to quickly choose an account of their preference. Additionally offer an option to load from RuneLite home directory, as well as load from a custom path.

[Z-Kris]

Completed in #30