merged

add report script for Mirabelle

Mirabelle: actions are responsible for handling exceptions, Mirabelle core logs only structural information, measuring running times for sledgehammer and subsequent metis invocation, Mirabelle produces reports for every theory (only for sledgehammer at the moment)

removed errors overseen in previous changes

moved Mirabelle from HOL/Tools to HOL, added session HOL-Mirabelle

removed unused signature

explicit checks;