Rework TLS configuration
Add new TLS configuration options to sample file
Read & apply configured TLS version & cipher list
Add TLS protocol configuration support to client

This commit also adds a `-tls-version` argument to the CLI interface in
order to select a TLS protocol version when using it.
Add note to Python client about TLS versions

Python 2.x doesn't do anything higher than TLSv1...
CI: Require `ssl-0.4.7` & update seed image
Doc: Add new TLS settings to documentation
Enhance TLS key and cert configuration checking

Result of the review in PR #461.

See: https://github.com/Incubaid/arakoon/pull/461#discussion-diff-14136674
Merge pull request #461 from Incubaid/tls-settings

Add TLS version & cipher list configuration