Ownership UI for org members list, plus general list improvements

The primary point of this MR is to add UI elements for managing organization account ownership to our organization members list view. It adds a mat-chip identifying the org account owner. It also disables the remove/leave button for the account owner, since owners may not leave their organization until ownership is transferred to someone else. When disabled, the button includes a tooltip with a note about this.

The layout of the member list view was already rather rough, especially for smaller screens where it basically looked broken. I have attempted to improve the general layout here. I am still not thrilled about the small-screen view, where I basically just stacked all the information in a column, but I think this is as good as we can practically get without a more time-consuming overhaul of the list.