backport improvements from promes_output project #254

To avoid having to release new versions of larray-editor for each promes_output new preview release, I used customized versions of ArrayEditorWidget (via inheritance) and some other components of larray_editor. These changes should be upstreamed to avoid as many as possible of these project-specific customizations.

On the top of my head, there is support for:

• not showing the filters layout
• not showing the options layout (decimals, colors, scientific)
• ability to retrieve multicombobox value explicitly (without listening on its changes)
• use new-style formatters for cell values ({}) instead of % (so that we can show thousand separators) and specific support for formats with commas as decimal separators
• better autosizing behavior (compared to 0.34) for the axes names/vertical labels columns EDIT: it is already done in 0.35