Implement a high-accessibility canvastable alternative
This loosens the coupling between AppComponent and CanvasTable, allowing us to switch between alternative canvastable implementations (which currently requires a page reload, given how interconnected everything still is). It also ships an optional simplified messagelist, using native HTML widgets which should mitigate canvas's inherent problems described in https://github.com/runbox/runbox7/issues/857.

The alternative messagelist is not fully functional (yet), but the basic functionality and styling are open to testing, criticism and patches.
Good initiative @tadzik!
Any particular reason the new view isnt an HTML table? its a little confusing as a list, especially when clicking "threaded" .. cant tell what that does at all - view just jumps/redraws
Couldnt see the "Next N messages" button at first - it disappears when the horizontal view pane is displayed
Up/down pages the messages (by 10) on the non-canvas list.. this is quite confusing/different to the canvastable.. Maybe that should be pageup/down instead?

Changing folders does not set the current page, so if I vist Sent, page forward a few pages, then visit Templates (or something with less pages), I get this view. I think the default should be to jump to page 1, when changing folders.
I could be missing something, or you lost it in a shuffle - when an email is open, there doesn't seem to be an indication of which one it is, in the mail list - row hightlight or similar

The Attachment / Flag columns are missing - I would think they'd be possible to do?
Have a look at https://material.angular.io/cdk/scrolling/overview to see if there are new strategies that are useful since this issue was last worked on.