Fix indexCreate for gapped Index. Note that it is no longer togally generic now (i.e. for ModReverse etc)
seqanLast runs, but fails of course at  the non existing S-Tree interface of the gapped index
Major improvement: Use MMap<> Strings instead of External<> String.
SeqanLast does produce output now. Correctness remains to be checked.
Inserted the gapped Index: now we need the S-tree interface for the gapped index
Deleted old test cases