feat: add smartcase support like vim

[phanen]

"smartcase": case sensitive if all chars in current query are in lowercase, otherwise it's case insensitive

I notice that there are two flags now:

• -case-sensitive by rofi globally
• -i used in rofi -dmenu mode
• So by default rofi is case insensitive, but case sensitive in rofi -dmenu mode.

This PR implement:

• Always use smart case by default like what fzf does (both in rofi and rofi -dmenu).
• To opt-out this behavior, users can still use -case-sensitive and -i.

[DaveDavenport]

Interesting patch, thanks!

[DaveDavenport]

If I understand the code correctly, this changes the default behaviour? It would be good (to avoid users annoyance) to keep the existing behaviour and add this as an extra option.