bring back user page

Adds a UserView that contains a MainSplit with an empty div
and a RightPanel, preset to the given member.

UserView fetches the profile and creates a fake member, which
it passed on to the RightPanel.

this doesn't use the view_user action on purpose, to avoid any
interference of the UserView when trying to view a room member.

res/css/_components.scss

@@ -10,6 +10,7 @@
 @import "./structures/_HeaderButtons.scss";
 @import "./structures/_HomePage.scss";
 @import "./structures/_LeftPanel.scss";
+@import "./structures/_MainSplit.scss";
 @import "./structures/_MatrixChat.scss";
 @import "./structures/_MyGroups.scss";
 @import "./structures/_NotificationPanel.scss";