Authority fixes

Closes: #417 (closed)

This MR also:

• completely refactors apply_authority_filter method
• renames rebuild_after_clearing_authority_filter into handle_filter_cleared
• adds _create_widgets_to_mount to AccountCollapsible
• changes moment of applying filters - it was moved from rebuilding all widgets to update methods
• merges MemoItem and Authority item into one class
• manages display of all widgets instead of rebuilding them every time
• rename AuthorityType into AuthorityRole
• rename Authority screen into AuthorityDetails
• rename RemovePrivateKeyButton into RemoveKeyAliasButton
• rename _update_authorities_and_suggestions_after_account_in_filter_changed into _handle_selected_accounts_changed
• rename AuthorityRoles into AccountAuthorities
• adjusts some docstrings