ctiapp: validating NethVoice enterprise subscription for app activation

[Amygos]

Validate if the Nethvoice mobile application is used for a Nethvoice instance with a valid Subscription.

PRs:

• https://github.com/nethesis/nethcti-server/pull/305
• https://github.com/nethesis/nethinfra/pull/199
• https://github.com/nethesis/ns8-nethvoice/pull/146
• https://github.com/nethesis/ctiapp-authproxy/pull/6
• https://github.com/nethesis/nethvoice-cti/pull/208
• https://github.com/nethesis/nethcti-server/pull/306

[Stell0]

Before merging https://github.com/nethesis/ctiapp-authproxy/pull/6 we need to backport https://github.com/nethesis/nethcti-server/pull/305 to nethcti-server on NS 7