Let the Foot inset have a different Layout when inside a title
This allows to address two main issues
* \thanks does only accept one paragraph, while \footnote allows several (ticket #2666)
* footnotes in titling environments were not numbered on screen.
Moreover, the code reduces hardcoding of features, which is always a good thing.
There are several pieces in this commit:
* new numbering type \fnsymbol for counters
* the Foot inset changes its layoutName() to Foot:InTitle when inside a paragraph with InTitle property. This is set when running updateBuffer.
* Foot:intitle uses the \thanks command, does not allow multiple paragraphs and marks its contents as moving argument.
* The InsetLayouts for Foot now have properLaTeXName/Type, so that InsetFoot::latex can be removed; further code simplification is probably possible.