modify group_cancel simprocs so that they can cancel multiple terms at once

"isabelle options" prints Isabelle system options;

removed leftover from 89cc3dfb383b, hoping that mira digests it;

discontinued presumably obsolete attempts at doc-src testing (cf. 3b02b0ef8d48, 89cc3dfb383b);

more precise imitation of old ROOT.ML files;

fixed mira.py (cf. fe611991427a)

corrected session name

removed obsolete mira configurations -- covered by AFP_images

modernized mira configurations, making use of isabelle build

removed mira configurations related to old importer

re-introduced ROOTS catalog files (cf. 47330b712f8f) which help to organize AFP or make -d options persistent;

more on isabelle mkroot;

added mkroot: prepare session root directory;

prefer general Command_Line.tool wrapper (cf. Scala version);

simplified Session_Tree; tuned messages;

some timeouts, which modify the build order;

queue ordering by descending outdegree and timeout;

tuned import;

clarified Session_Tree (with proper integrity check) vs. Queue (with provision for alternative ordering);

clarified Session_Entry vs. Session_Info with related parsing operations; more error positions;

simplified class Job; tuned message;

let with_timing report overall number of threads;

further robustification of interrupts during build;

refined outer syntax;

prefer calligrapic \<RR> \<II> over \<Re> \<Im> for "screen" display (NB: official unicode defines only one version of these glyphs, unlike TeX);

remember ATP flops to avoid repeating them too quickly

remember which MaSh proofs were found using ATPs

rule out same "technical" theories for MePo as for MaSh

don't generate queries for empty dependencies

crank up max number of dependencies