[2.1] Stop supporting ubuntu trusty for GUI?

[julien-duponchelle]

I propose that we drop support for ubuntu trusty in 2.1.

Trusty is no longer the current LTS release. Xenial replaced it.

Their is mostly two changes interesting:

• Python 3.4 (Xenial: Python 3.5)
• Qt 5.2 (Xenial: Qt 5.5)

I think dropping support for Qt 5.2 could be a benefits. We see from @AJNOURI that we have multiple issues with this version:

• [2.0] small GNS3 topologies hogs lots of memory #2047

I propose the change only for GUI, because the GNS3 VM still use trusty.

[julien-duponchelle]

Another benefits we could use websocket to connect to the notification avoiding the need to trick with an HTTP stream. It's a new feature of Qt 5.3.

This could solve the random disconnect from project that we see with aiohttp 2.0

[julien-duponchelle]

See also #2084

[grossmj]

I am ok to stop supporting Ubuntu trusty.

[grossmj]

@noplay now