gui: fix crash on loading arbitrary blockset file

Example:
$ qnpge blast_hits.bs

It used to crash because it tried to load global blocks.
AllProcesors: print default values of options
comparison operator for Block and BlockSet
update example of script in API.md

Use new script syntax
complex script example in API.md
rename MakeSubPangenome <-> SubPangenome
Pangenome: finally OverlaplessUnion(Blast)