Horizontal panel - general

[isidorn]

• win @dbaeumer
• mac @egamma
• linux @jrieken

We introduced a concept of the horizontal panel to the workbench. For specific output and repl functionality there is #2176, so no need to test that. Verify:

• You can toggle the panel, either from the view menu or using the shortcuts
• You can nicely resize the horizontal panel using the sash which causes smooth layouting
• When opened horizontal panel always restores it's size and opens the last active panel (repl, git output, task output)
• Horizontal panel has a maximum size, and a minimum size below which it is minimized like the sidebar
• Be creative and try to break the workbench layout by minimizing / maximizing components, moving sidebar to the right, toggling visibility...