Selectively display sections in right panel

**Is your feature request related to a problem? Please describe.**
I am trying to use gdbgui for debugging bare-metal ARM code running in QEMU.

There are a lot of display sections in gdbgui right panel which do not make sense in this use case.
I am especially interested in the register panel contents, which gets pushed out of view each time.

**Describe the solution you'd like**
I would like to be able to control which sections are enabled and displayed, as well as the ability to rearrange the sections.

**Describe alternatives you've considered**
Make the right panel occupy the entire height of the window to provide more space.

**Additional context**
I'm running on macOS Mojave, with multiarch gdb 9.1 and qemu 4.2.0 installed using MacPorts.

The issue names no files, tests, or entry points. Start by tracing the frontend's right-panel section rendering and register-panel placement; done means users can choose which sections are visible and rearrange them without losing access to the registers.

Written by the indexing model from the issue text.