Do not request a new connection token at each "run"

[LucaGallinari]

Is your feature request related to a problem? Please describe.
The plugin request a new connection token to Akeneo at each "run". Akeneo stores these token in internal tables and they can grow in size pretty fast even you remove the expired ones.

Describe the solution you'd like
The system should save the token and use it until expiration instead of requesting a new one at each "run"