Re-add support for passing `title` as string

[emilykl]

• Re-add support for passing a string to title property (removed in #7212)
  • Other properties removed in that PR (e.g. titlefont, titleoffset) remain removed
• Re-add functions for moving title string to title.text internally
• Re-add Jasmine tests for passing title as string

[archmoj]

We should possibly support this option on places e.g. legend.title. No?

[emilykl]

We should possibly support this option on places e.g. legend.title. No?

Agreed, it makes sense to be consistent, I'll look into how much work this would be.

[archmoj]

Revised in #7262.