[FEATURE] Added custom widget for titleCompact and footerCompact

[BranislavMateas]

Hey!

So playing with this package, I came to this problem, when I wanted to render different widgets for footer and title depending on the displayMode. I tried using providers, however, to make it work properly I needed to add addPostFrameCallback, which impacted performance (by rendering widgets late - I couldn't render it faster, as I can't call setState during the build phase), so I decided to make a new feature, that would solve this problem in a non-robust way - with adding titleCompact and footerCompact, which if not filled will not affect rendering of the footer/title. Hope you like it! (and merge it 😁)

Signed by Branislav Mateáš.

[Jamalianpour]

Hello and thanks,
But sorry it's not in my strategy. If anyone want to change tittle and footer in SideMenuDisplayMode.open or SideMenuDisplayMode.compact can use onDisplayModeChanged and then change his/her widget.