keybinding improvements

[edmundlaugasson]

The idea is very fine. Following is based on TreeSheets-e3b4ae2-x86_64.AppImage (January 29, 2020), although it exist also in September 2, 2019 version of Treesheets. Some more ideas how to improve it:

• add search bar to quickly find appropriate item
• add start searching when typing - not only first letter but as many as wanted. E.g. Midnight Commander in Linux has such search (you need to disable terminal line in first place from its settings: Options->Layout and remove [ ] Command prompt selection by space) - I can type several letters and also delete them one by one and I see below in status bar my typed characters and its deletion when I delete. Similar behaviour would be nice to see also in Treesheets.
• show current keybinding in additional column without opening item
• make scrolling with mouse to work - currently it does not (with version September 2, 2019 the scrolling works)
• categorizing by menus - allow this to be configurable option: flat mode like currently (all choices in one column) or categorized by menu names
• when closing exact keybinding dialog - don't close overall dialog. Probably there is a need to see next keybinding. Every time I open exact keybinding and close it - there is a need to reopen that keybinding change dialog again.

[aardappel]

The keybinding is built from fixed wxWidgets dialogs, wxSingleChoiceDialog and wxTextEntryDialog that allow very little customization. Short of re-writing all this functionality myself, the above will be a lot of work to add.

The idea was that keybinding is an infrequent operation, so a simple UI would be ok.