Message list/pane: Context menu for msg actions

[castaway]

Is your feature request related to a problem? Please describe.
On large screens the message action menu requires a lot of mouse/eye travel to use

Describe the solution you'd like
In addition to the existing message pane action menus, could we add a right-click context menu for easier/quick access to the actions. This could also appear/be useful in the message list without opening a message

Describe alternatives you've considered

Additional context
Suggested by someone on the forum: https://community.runbox.com/t/suggestion-adding-message-actions-in-a-right-click-menu/483

[castaway]

Could either use Angular cdk: https://material.angular.io/cdk/menu/overview though I think we'd be better off with something that extends the existing browser context menus, eg: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/menus