make mkSimpleMenu more general

[cortsf]

Such that rofi can always be called using this function. This simplifies code and makes it easier to allow users to set a custom font size for all rofi menues, and such.

• Return a dict including the selected item, index, filter string, etc (see rofi's --format)
• Take a collection of additional keybindings (such as -kb-custom-1), with each item paired with a corresponding callback/lambda function.
• Provide a mkPrettyMenu wrappper allowing to include a "doc only" paragraph on each rofi row. Return first paragraph content instead of the whole (two paragraph) string (check call_rofi_submenu)