Better env checking

[rishson]

Runner should:

• check the analysers to run.
• check each analyser's runtime lang
• only run valid analysers

e.g.
for sidekick-rubocop, make sure that ruby is installed.

we could have a requirement for a script in bin that checks all is OK?

e.g. bin/valid

if command -v "ruby" >/dev/null 2>&1 then
  echo '1'
else
  echo '0'
fi