- new DrawForceChanged command to force recomputation of vertex arrays

* New version of Trevor Strickler's QuadTri patch (+ examples in benchmarks/extrude_quadtri)

* First pass at SU2 mesh export

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New homology command "Betti" to compute just the Betti numbers of the given domain and relative subdomain. It is always somewhat faster than computing (co)homology basis.

- remove error in a:b:c if leads to empty list

To abort a script, use "Abort"

Better handling of (co)homology computation in selected dimensions only. Various cleanups and documentation of (co)homology stuff.

fixed nasty bug in quad meshing
added parameters to BL generation (2D)

Make sure to close the files left open (on purpose) in ParseFile when we exit OpenProject or when we call ClearProject.

Leaving the files open can lead to file handle exhaustion, e.g. with onelab when remeshing several hundred times. This then leads to
unpredictable socket errors.

First pass at cleaning up lists in the .geo parser: 

- we now keep track of the variable type ("list of floats" or "single float")
- the brackets [] after the variable id are now optional (aa={1,2} == aa[]={1,2}) when creating a new list
- the old syntax is kept to enable forcing the type to "list of floats" when creating a single-entry list
- on single floats, += performs the usual arithmetic operation; on lists, += appends to the list (idem for -=)

WARNING! this is a possibly dangerous commit: please test your .geo files and your scripts and signal any weird behaviour