Add panel for apps in app.html

Note: I don't know what to name this panel yet so I just ended up going with panel as there is no collision in file names elsewhere.

This MR introduces some changes to the app.html layout, mainly:

• A new panel is created to hold action buttons
• Launch button is now shown in the panel alongside "Client Apps"
• Run Diagnostics button is moved into this panel as well.

This PR aims to fix #1690 (closed), #1713 (closed) and #1698 (closed) (partial)