Refactor/merge Visual and Panels mode

[XVilka]

Currently, both modes are implemented completely independently, sometimes with code duplication/copy-paste.
I propose to reduce the code and feature duplication by:

1. Migrate Visual mode from commands to the API: Refactor Visual mode (librz/core/tui/visual.c) to use API instead of commands #382
2. Migrate Panels mode from command to the API: Refactor Panels mode (librz/core/tui/panels.c) to use API instead of commands #383
3. Migrate Visual menus code from commands to the API: Refactor Visual Menus /librz/core/tui/vmenus* to use API instead of commands #491
4. Only after the three above are finished, determine what code is logically/semantically share by both and extract it into other file or RzCons or RzUtils.
5. Determine what features overlap, and consider the merge of both modes.

Please note, that many features that are present in Visual mode are missing in the Panels mode, and there is a significant difference how these modes operate:

• Visual mode has the concept of rotation - press p/P to switch between representations
• Panels mode has the concept of panes and useful for custom arrangement.

Thus, we might consider keeping the both modes as is from the user point of view, but reduce the code and feature duplication to the minimum.

[ret2libc]

I think this is not going to happen anytime "soon" and by soon I mean at least a year, considering the many projects we have opened right now. I propose to close this issue for now as a way to try to keep the list of issues manageable.

[XVilka]

No, it's important issue and there is a lot of duplicated code.