Removed mention of convergence from CBFrontend, made trust decision cache resizeable and use available space.
Added some further error handling to linux ping call, removed superfluous debug outuput from plugin tracer.
Added notification page for untrusted certificates.

This may still need some more checks, but it's better than silently aborting the page load.
Extended build script.

Now creating a version.txt file containing the build version, host and
build time.
Merge branch 'master' into remove-ooni
Fixed some bugs in PyBear.

- Passed wrong URL with missing / to verifier
- Added missing imports to Verifier
- Fixed error when number of URLs is smaller than sample size
- Fixed incorrect call to resolve_ips() (Curse python's explicit self)
- Corrected error when no IPs are returned by resolve_ip.
- Corrected trim() to strip().