[FR]: Select specific account upon start

[RetroAbstract]

Brief description of the feature request

This feature would allow the user to display articles of a specific account upon starting RSS Guard.

This could be implemented with an account drop-down selector in a toggle setting: "Tools" > "General" > "Select account on startup: [Selected Account]".

When enabled, RSS Guard would select the set account on startup, resulting in displaying the articles for that account in the article list.

When disabled, RSS Guard starts as it does now and doesn't display any articles for any account in the article list.

Thanks!