It makes it easier to browse tgba/.

* src/tgba/state.hh, src/tgba/succiter.hh: Delete, and
move the contents...
* src/tgba/tgba.hh: ... here.
* src/tgba/Makefile.am: Adjust.
* src/graphtest/ngraph.cc, src/kripke/fairkripke.hh,
src/saba/sabacomplementtgba.cc, src/ta/ta.hh,
src/tgba/tgbakvcomplement.cc, src/tgba/tgbasafracomplement.cc,
src/tgbaalgos/bfssteps.hh, src/tgbaalgos/emptiness.hh,
src/tgbaalgos/gtec/explscc.hh, src/tgbaalgos/gtec/sccstack.hh,
src/tgbaalgos/rundotdec.cc, wrap/python/spot.i: Adjust includes.