cyclades: Invalidate snapshots when job fails

Make Cyclades invalidate snapshots in case of failure to submit the job
to Ganeti, or when the job fails. In either case invalidation is
performed by marking...
TODO: Add states sto API

fixes grnet/synnefo#231
admin: Migrate from Highcharts to C3

For every chart that uses Highcharts, add its C3 counterpart below it.
The change from Highcharts to C3 is for license reasons.
admin: Lift restriction on charts

Remove `ADMIN_ENABLE_CHARTS`, as we now use C3 instead of Highcharts.
docs: Remove Admin charts section

Due to the migration from Highcharts to C3, the charts are now enabled
by default.
Revert "cyclades: Invalidate snapshots when job fails"

This reverts commit 0d1b405df358e17e369d910edc0fa9977b12bfa9 that has
been accidentally pushed remotely.
Merge branch 'release-0.16-admin-charts' of https://github.com/apyrgio/synnefo into release-0.16
astakos: Fix license of astakos/admin/users.py
astakos: Fix pep8/pyflakes issues
deploy: Remove version dependency to curl