Add support of gantt and process views in GTK client

Registered by Joël Grand-Guillaume @ camptocamp

As the webclient implements the Process view and the Gantt view, I think that the GTK client should also handle those views...

Blueprint information

Status:
Not started
Approver:
None
Priority:
Undefined
Drafter:
Joël Grand-Guillaume @ camptocamp
Direction:
Needs approval
Assignee:
None
Definition:
New
Series goal:
None
Implementation:
Unknown
Milestone target:
None

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